depends on how big the case is. if it is tiny, then sure. if you have a larger mid-tower, then maybe. yes if you only surf the web and word process (yeah, that's likely... hahaha) no if you push it a lot.
it also kinda depends on the HD's you are using. my father's ibm drives tend to run REALLY hot. I'd say half of his cooling problem is the heat given off by his IBM's. the other half is a crappy case and fan setup.
you can treat the two fans on the whisper as one really nice fan. that said, you ARE putting the 80mm in front, right? if so, cool.
chances are that if the only fan mounts in your case are for those two fans, you have a pretty small case. in which...er...case (too many cases) you should be quite comfy.