I believe I would phrase it a little differently.... Stall speed is nothing more than what you read on the tach, when you lock up the brakes, and apply full throttle. It doesn't kill the engine... It's just the maximum engine rpm you can get, when the trans is 'locked'. And, the other posts cover the reasons for 'higher' or 'lower' stall speeds. What you want, or need, depends on what you are trying to do. Obviously, a higher stall speed lets you get into a more favorable engine power-area, if you are trying to 'launch' well, as for drag-racing. Down-side.... You'ld be running in the 'slip' zone most of the time, at 'street-rpm's'. A 'low' stall converter locks up early, but hampers 'launching' capability, because the engine doesn't want to make much power/torque at low rpm's. 'Stock' works pretty good for most folks, even off-road, and in 'rock-crawling'. Like CJD suggested, it's a trade-off between 'slipping' (the equivalent of lower gears), and locked-up enough that you can live with it for other situations.