Another dumbass question: Has anyone run multiple instances of miner clients and had it stay stable. I want to use seperate cards in same box so I can try Vertcoin. I realize I might have to upgrade memory capacity for that box. I know cgminer has an option to select cards to use ... just have not dug into it yet and do not want to make my mining box unstable trying this.
Yes, that can be done. I had an experimental box that ran vertminer, cgminer HVC fork, and sgminer for scrypt each on its own 270X card. "device" option allows you to specify which cards to use, and "remove-disabled" hides the cards you don't use (so that multiple instances don't interfere with each other). Also check "api-port" - you might want to specify different ports if you are using some kind of monitoring software, and set up said software accordingly. I would suggest to tune the miners one at a time, and only start multiple ones when you are sure they work properly.