SLI is a PITA in my opinion. FYI, I just built a really nice machine. I'll pass the specs on to give you something to mill over:
Antec 900 Case (with the two optional fans, and a PCI slot cooler)
Zalman 9700 NT (with arctic silver 5)
Q6600 @ 3.6 GHz, 66*C hottest core under full load
EVGA 512 8800 GTS G92
4 Gig G.Skill
Gigabyte GA-X38-DS4
150 Gig Raptor 10K RPM
PC Power and Cooling 750 watt PSU (overkill for this setup, but I wanted the stability/reliability)
This rig is realistically the fastest one can get their hands on, short of SLI or Crossfire, both of which I avoid. Plus, with the 9800 dual GPU coming out in Feb, I could care less about dual/triple/octo card setups.