If you're after performance, do yourself a favor and pick up a newer aluminum head engine V6 for a rebuild.
I was going to do a performance build 3.4L out of a Camaro, which uses the same heads as us just on a bigger engine, but I've done a lot of homework and I couldn't bear to put another set of iron heads on my car once I saw what the aluminum heads and intakes were able to improve on comared to our setup.
Please refer to this thread on the Full Throttle V6 forum as to what the benefits are to switching, it also has pictures to demonstrate the design differences, hope it helps.
http://www.fullthrottlev6.c...howthread.php?t=6752If you want a little more power but want to stay stock, then keep your heads, but put them on a 3.4L bottom end from a Camaro, you'll be picking up some decent power, and you can free up a little bit more by porting and polishing the heads, porting the exhaust, adding a new camshaft, and then tuning it.