Lots of answers, maybe just not the ones I want to hear. The 12mm thick scythe fans are little bit pricey compared to some competitor 25mm, so I could stick with just one 120 on the side and leave the the other open to the air, or go ahead and suck up the prices of the 12mm and put two of them on the side (ocd like that. one 25 and one 12... Not gonna work for my head.)
Though I did mention that some one said that blowing air into the Zalman like that may just impede airflow, and I can see where he is coming from but even in that case it seems like it would still make sense to have an exhaust fan over the Zalman and suck the heat right out of the fins.
Thanks everyone for your feedback. Taking all this to heart. I intend on keeping this system this way for a long time, with minor upgrades, and I want it to be right. Starting to think the only way I'll truly have my answer is to buy the 12mm fans and test for myself.