[Wintermute]

First, I don't see a problem with completing from the SB with this hand in a 4-handed game occasionally. You just have to exercise discipline postflop when marginal boards come.

The main problem with the postflop action is that the spades kill several of your potential outs. Also, having an non-spade 8 fall will only guarantee you half the pot anyway (I don't buy your claim that you know nobody has A3), and a non-spade K won't give you the nut straight. If you make the turn a 4 of clubs, then I might be more willing to go to war given that this sounds like a game where people aren't necessarily trying to play optimally... but with this board I would fold--if you count up outs you'll be able to convince yourself it's -EV.