I've just got my new PC last week,
Vista oltimate 64 bit
Intel® Core™ i7-965 Extreme 3.2GHZ 8MB Cache
RAID 0- 600GB (2 x 300GB)SATA 3.0Gb/s 10,000RPM 2 x 16Mb Cache
12GB DDR3 1600 MHZ OC PC3-12800
Dual 2GB GDDR5 ATI® Radeon® HD 4870 X2 in crossfire.

I did a test on M2TW, it was a 2x2 custom battle against AI, with my own modification of unit size (I made most of the units 253 men each just for this test), a total number of more then 16,000 men on the field! It got a bit slow after the fight started but still playable. That was a good fight, make you really feel is in the battle field. Unfortunately I don't know how to attach a picture here.

I just hope ETW can at least given us the option of using a bigger unit size for 250men+.