My personal opinion is that it's basically better to stick with the system you already know, otherwise you'll only have a lot of trouble and loss of time by having to completely re-learn the system and its administration.
By administration I don't just mean the usual clicks on the interface or surfing the internet, but how to administrate the device, how to secure it, how to get backup and disaster recovery reliably under control.
If you haven't got it right with the PC, it's certainly not going to get any better or easier with the Apple, because you start from scratch.
Maybe you have already bought some additional commercial applications for the Windows PC that you might not be able to use on Apple, that would be all lost money and know-how.

In the Apple area, not everything that shines is gold:
1. prices: at Apple you pay a lot of money for commodity hardware and the prices escalate even more when you start to equip a system with the more powerful components.
2. ergonomics: Apple screens do not have anti-reflective screens for years, for me a clear no-go.
3. if you look at the values in DAW-Bench then the Windows audio system has always been a bit better than Apple's and from what you read (of course it can be wrong, so it's better to find out beforehand) then Apple Core Audio has higher latency values compared to ASIO drivers under Windows.
4. regarding RME: if it works and there are no problems with Apple's USB stack or new communication chip, then it should work without any hassles, of course.
Only that RME does not offer DIGIcheck's "Global Record" for Apple. If you have grown fond of this light-weight recording tool in any way, or if you can't rule out using it as an alternative to DAW recording, it's only available for Windows. The last updates at Apple led to incompatibilities with DIGIcheck, RME is already working on it, but there are no fixed dates when it will be finished.

Since Apple devices are more expensive per se, I would rather use this money to get a Windows based turn-key system for recording from the appropriate companies (Xi-machines, etc).
And if you don't necessarily need a laptop, then you better get a desktop system, you are much better off with it:
1. better performance and scalability
2. no reduced chipsets or CPUs for energy saving / thermal reasons
3. component selection up to the most powerful CPUs possible, much more choices compared to Apple (Intel Desktop, AMD, Intel Xeon)
4. no thermal problems under continuous load, which usually throttles down the CPU clock very quickly on laptops if it gets too hot in the narrow case
5. much more possibilities in the BIOS to disable power saving functions with the goal to minimize the DPC latencies, so that the CPU can react more responsively to load situations and one can get along with a given workload / CPU load also with smaller (ASIO) buffer sizes.
6. possibilities with dedicated PCIe USB cards to decouple the recording interfaces from the rest of the USB infrastructure in case any USB Blootooth adapter or USB hub should cause instability.
7. the easier and cheaper way to use PCIe cards, if you want to work with lower buffer sizes at higher system load than if you have to buy expensive external Thunderbolt Cases offering PCIe slots.

As I said, these are my personal $0.02 and I hope I do not offend any Apple user by these statements/recommendations.
If you like the Apple Philosophy and Style, I am completely fine by this.
If you ask me from technical perspective, this is my *personal* opinion.
Like always .. your mileage may vary...

> What buffer settings can I expect to use reliably ?

This always depends on the project, how many CPU power it requires ...
And whether you need more CPU cores (with automatically lower CPU clock on average) or higher single thread performance (high CPU clock but then usually lower amount of CPU cores) depends on whether you simply have a lot of tracks or whether you have many inserts per tracks, because all the VST's need to be processed one after the other in time and the results have to be in synch with the rest of the tracks.
You also need to look / check / ask for consultancy if you intend to work with highly CPU consuming VST or a lot if VSTi (virtual instruments).
Therefore the advice .. get in contact with specialists who did all this testing already and know their hardware and built stable systems with good drivers.

RME drivers are highly optimized and RME doesn't use 3rd party communication chips.
Therefore every RME driver is fine and delivers stability and low latency.

You can look at these two blog articles, one containing a table with different Round Trip Latencies of different RME solutions:
https://www.tonstudio-forum.de/blog/ind … 8-RME-UFX/

In this blog article you can see how stable the setup is even under higher load:
https://www.tonstudio-forum.de/blog/ind … cks-de-en/

If you want peace in mind for a long time and an interface with all RME features then take UFX+ like I did or UFX II.
If you prefer PCIe, then get RayDAT,  but this card has no analog I/O port ...
AIO is not the proper choice, it has only one ADAT port.

I would sell UC and get UFX+, then you can use USB3, USB2 and Thunderbolt.
Thunderbolt is external PCIe ... with this interface you have most options.

The new MADIface USB driver even support ASIO buffer sizes down to 32 samples, the older USB driver has 48 as lowest setting at 44.1/48 kHz. This also gives you more options. Thunderbolt driver has the special feature to support also the pitch function of the driver, which is not possible for the new USB transfer modes.

AS UFX+ / UFX II are the flagship interfaces from RME they have every cool feature like: AUTOSET, DURec, FX chip etc.
MADI is nice to have as an option for scalability if needed. Higher cable length more channels which is nice, if channel multiplexing is needed for higher sample rates. With ADAT you loose to quick too many channels.

And MADI is also nice for remote controlling RME devices, because you can do this via MIDI over MADI, which makes a MIDI cabling for remote support completely unnecessary.

You can use an USB/Thunderbolt interface for both .. laptop and desktop -> highest flexibility and
sustainability of purchase and money spend.

> I can tell you don't know much about Macs, Ramses.

Hi Cy, sry, but this is not the point. I simply have other priorities than "zero configuration" and I think I made my position clear.