Just got my RME UFX. Really amazing product!!
My Motherboard is ASUS p8p67 Deluxe with one 1394 (VIA VR6315N chipset 1394), 4 USB3 with NEC uPD70200chips, tons of Intel USB2. Win7 64bit.

From cross comparison by playing 44.1Hz 16bit music using direct stream with foobar2000, at lowest latency the 1394 sounds best with better punch and details. Front board USB3 is worse, backboard USB2 is similar to 1394. Just when I decide to stick to 1394, the weird thing happens.
(I don't know why but maybe the front board USB3 bay may not be that good)

The testing project is 44.1kHz 24bit full of high latency plug-ins (Nebula Reverbs with 8192 dsp buffer) under Rear 4 64 bit.

Before the project is mixed under Echo - Mona 4096 samples latency, and the playback is fine.

The problem is under 1024 samples maximum latency using 1394 firewire, the project eats all real-time CPU, so the playback is jaggy and full of drop out.
Then I try the USB2 and hope there are higher latency settings, I find 2049 samples could playback my project. And then I decrease the latency to 1024 samples, the project could still playback smoothly. The playback is more responsive than playback with Echo Mona.
I'm glad it plays smoothly or I have to find another interface quickly.

I always thought that 1394 has better performance than USB 2 and less interference from other connected devices on the chipset.
Is it normal or the onboard 1394 chipset is bad??