Hi!
Well basically i can give you some perfect examples.

Reverence being a prime one. At anything under 256 buffer on bootcamp in cubase i get the asio meter first clipping, then going wildly erratic even in an empty project with one instance. (on OSX it's a nightmare)

A second perfect example: DDMF's excellent linear phase mastering EQ, LP10

In studio one on OSX i cannot even get ONE instance of this to run without the cpu being in the red, in logic it uses 20% with no spiking, of course due to logic's internal buffer.. but it's stable.. on cubase bootcamp same thing as studio one OSX and CUbase OSX... it goes nuts...

A third example. Voxengo elephant in 8 x oversampling.

A 4th example, melda linear phase auto equalizer (even with no oversampling)

Logic handles all these with ease whereas none of the other hosts i mentioned on either platform do. That's why i was specifically wondering on a proper custom built daw pc from a professional, with a pcie rme card, if cubase can handle these plugins at low latency.

as you can see from the examples i've given it's basically plugins with large latency which cause the problem. Fully functioning demo versions are available for everything i've listed. Of course there is more, but i think that's a good starting point.

meldaproduction.com
voxengo.com
ddmf.eu

if i raise the buffer to 1024 on cubase it can handle these ok on OSX, acceptable... studio one still shits itself... logic the best of the lot.. This is why i specifically need to know how windows 7 deals with them with a good pcie card.

FWIW i'd initially plan to run cubase 5.5.1 in X32 mode but in Windows 64 professional (mind you i wonder if windows 64 professional is not the right choice? that's all i've got to test with)