it isnt any worse on the car mechanically if you keep it from knocking and running in good health.

with a 3.4, the car FEELS twice as fast, even though it isnt. id say with a little colder set of plugs and the tune with the PCM that youd be good with a 3.4. id be willing to say that you could run a 3.5 very easily (just for your knowledge, as a performance package SLP gave a grand prix GTX a 3.5 pulley).

if youre that worried about it, grab a powerlog while youre looking for a PCM.