so in case yes you should get a i7 920 and 6Gb of ram, if you can aford yourself, but the pc you listed are good enaugh also with the i5 750 actually you would not have such a problem with heat temperature like with an i7. But if you are looking for really good performance and the maximum of the maximum take the i7 920 (D0 Stepping) and Overclock it.^^
I bought the i7 920 now 4months ago in D0 stepping 83 Degrees (Load) with intel boxed cooler.
But with the corsair Watercooler for 80€ i've got it to 36 Degrees under load^^
so i just went furder to oc it now i have temperature like 55 Idle and about 68C on Load.
And now the best i have overclocked it from 4x 2,66 to 4x4,8Ghz with an Intel Mainbord DX58SO.
So i can not tell you what to buy but for better performance use i7
for good performance and an idle system temperature use the i5
if you have any more questions just write me a personal message or write furder in the Forum^^
Yes, but i meant combined, for example lets say that the OP mostly plays games on his PC. He would be better off saving that 120.00$ for a better GPU as opposed to the 860 unless he plans on leaving the clocks at stock. IDK, i would opt for a 750 and a nice air cooler. I was lucky enough to get one from MC at 149.99$, at that price there is no better option.
The 750 has VT-x but no VT-d, and that supossedly is a must for some :