I3 540 3.06 ghz for i7 920 2.66 ghz

The 920 is better but it fits in a different motherboard and neither will hold back a 450

hmm...what if i upgrade to a gtx 550 ti?
will any of these be bottlenecked?
and why will the 920 fit in a different motherboard?

Best answer selected by chineerulz.

You won't bottleneck GTX 580's in 3 or 4 way SLI with an i7 920. The 920 is a monster still to this day. It's easily overclockable for big performance gains. Took me 5 minutes to get mine from 2.66 to 4.0 for basically a 50% jump in performance. As mentioned above, the problem for you is you'll need a socket 1366 motherboard and triple channel memory.

If you're going to do that, some (myself included) would probably almost push you to buy an i5 2500K with a socket 1155 board for 3 main reasons. 1) You could reuse your dual channel memory on that board. 2) 1155 boards are cheaper than 1366 boards. 3) 2500K > 920 for gaming purposes. I'm not sure what he's selling it for, but you can pick up a brand new 2500K at Microcenter for $180. The 2500K is also a GREAT overclocker. Much better than the 920.

To sum it up, depending on what your buddy is selling the 920 for, I'd bet that upgrading to a 2500K and 1155 board would be better for gaming, use less power, and be cheaper than upgrading to a 920, 1366 board, and triple channel memory.

Check that, it WILL be better for gaming and use less power. Whether or not it's cheaper depends entirely on what your buddy is selling his 920 for.