Some good advice has been posted here already but I'll weigh in as well.
If money is no object, the 8800GTX boards are simply the fastest graphics boards on the market at this time. These boards are not "bang for your buck"...they're just "bang".
I've not yet run SH4 on mine because I don't have the game but at least one user on this forum has already reported running SH4 on an 8800GTX without any problem. I can say that I have yet to throw a game at this board that it can't handle, all settings maxed with performance to spare.
A couple of caveats...as already pointed out in this thread, you will definately need a better power supply and this can be a tricky thing to pick out. Another issue not already mentioned is that the 8800GTX has a longer form factor than most video boards and clearance can be a problem inside a tight chassis like the ones from HP.