I've kept a 15" common with smaller & adult bristlenose before without problems. I've seen aggression between adult male bristlenose before, but not between bristlenose & commons.
Exellent. Thanks for the fast reply. My girlfriends bristlenose has been getting rather chewed up and the only option is to move it to one of my tanks and since I have a malawi tank and a community tank i need to put it in the community tank and there is a small (2") common plec in there already...