I think i7 currently is totally overpowered for games, because they cannot fully profit from its new architecture. Thus, most games will not run faster with an i7 in comparison to a C2Q. Beware that there are only highend mainboards available for a an i7 platform, which cost almost thrice as much as a good P45 mainboard. The reason for this is that impatient customers will buy mainboards which they actually don't need. Yet it will take some time before consumer boards for the new generation will be introduced to the market (milk those who cannot wait).
On the other hand the socket 775 and the Core2Quad architecture will no longer receiver further updates and will peter out sooner or later. CPU wise you now have to choose between a highly expensive system, from which you might not distinctly profit, or a sufficent system, which will be outdated sooner or later. There also is AMD's new PhenomII, which is newer though not significantly faster than the C2Q architecture. Y
et CPU's last much longer than graphic cards, which have to be replaced every six months, if you always want to play on top notch settings at a high resolution (1920x1200, 4xAA, 16x AF e.g.). A single gpu is preferable to a multi gpu system with regard to power consumption, heat, noise and microbursts.
If you focus on Black Shark, a high end system is not too important. This game looks good but is not as power hungry as GTAIV or Crysis for example. I have run a brief peak on my system:
CPU: E7200 @ 3200 Mhz
MB: Asus P5Q Pro @ 400Mhz FSB
RAM: 4096 MB @ 800Mhz
GPU: Sapphire Radeon 4870 512MB
Black Shark Settings: 1920x1200, ingame maximum quality, 4x adaptive AA (edge detect), 16x AF, rest set to maximum quality
So far the game runs very smoothly, but I have not tested it in detail yet and may have not encountered a situation in which there was not enough power. Thus I conclude an i7 and a GTX280 may not be necessary.
In the end the decision is up to the tasks you need to with your computer and only you can give an answer to that question.