Welcome to AT
SLI boards are stable whether you run either one or two cards...and any instability is from the drivers not the hardware(which is pretty much worked out by now and rock solid, albeit a few old games, everything will run fine)
If you are not a heavy gamer i recomend and Nforce 4 ultra board, or even to save some money an nforce 3 ultra board, it all depends on if you are going PCI-E or not...
Gigabyte makes some very solid feature laden boards if you are not planning to OC...