CPU is the bottleneck at low resolution, whereas, the GFX is the bottleneck at high resolution.
The maximum FPS you can get at LOW resolution(1024x768 or 800x600) is equal to the CPU's max FPS potential with all GFX effects in game being off.
The maximum FPS you can get at HIGH resolution(1680x1050 or higher) is equal to the GFX's max FPS potential at that resolution.
The most common monitor standard today is 22" with 1680x1050 resolution and therefore most people tend to get a decent GFX with an OK CPU for GAMING purpose these days.
At HIGH resolution, you will only see benefit of a decent CPU like i7 with SLI or CF.
However, you would like to get a *decent CPU(E6300) with an OK GFX(HD5770) at 1280x720 resolution.
*In fact, E6300 is not decent but won't bottleneck HD5770 in either HIGH or LOW resolution. Thus, it's good to be paired with HD4890/HD5770.
i5 doesn't bottleneck HD5770 as well, but it's an OVERKILL at 1280x720 and so it's a waste to you.
################### NOT quite true, but kind of ######################
In most games, i5 is only valuable with HD4870 x2/HD5850/HD5870 and HIGH/LOW resolution.
However, in Crysis is i5 only valuable with HD4870 x2/HD5850/HD5870 and LOW resolution.