It wouldn't hurt to pick up a pair, there's some great Ultras on Tiger Direct for about 11$ including shipping (plus no tax, yay!!)
If you're not going to OC then you should be able to sneak past without one, but for 44$ you can get all 4 and then you don't have to worry about burning up ram.
(I've personally gone through about 3 sticks from that myself)
How big are we talking? Like a massive HS with a push/pull system?
I would just crack open the case and check it out visually, if it doesnt come close to the ram you're in the clear. If the fans or HS hang over the RAM check the distance you have from the top of the RAM to the HS fans, and go from that.