In general, I have had good luck with the SST, but I will say that those experiences probably aren't relevant for the caliber/charge consideration we're talking about here.

Based on my experiences with the SST, I'm not sure that a "light for caliber" SST at relatively low velocity would be my first choice. It's a great deer hunting bullet in 'standard for caliber' weights, and at 'traditional' or 'magnum' velocities (i.e. 30-06 150grn or 165grn, trucking somewhere around 2900fps from the muzzle), but if you're looking at a youth or compact 20" .308win rifle, flying somewhere in the 2200-2300fps from the muzzle with a 125grn SST, I'm just not sure the expansion and penetration are going to be what you want.

I WOULD be confident, that at 100yrds, a well placed 125grn SST will kill deer, even leaving the muzzle at a relatively low velocity, but I'd have to think about it more to decide whether it'd be my first choice or not.

If you go this route, please do report back on performance.