Yeah, so it's pretty clear one or both of the following are happening:
1.) the air is getting heated by passing through the front rad
2.) the single intake is significantly limiting total airflow through the case, reducing the air that the other three fans get
1.) increase airflow through the front rad
2.) increase total intake airflow by adding another fan somewhere
For #1, another 200mm fan in push-pull on the front rad will help. The Antec Big Boy is apparently a decent choice for this size of fan.
For #2, if you're able to do some modding to the case, cutting a hole in the case bottom about where the pump is and putting in another intake fan should help. Use a fan filter to limit dust intake.
Edit: come to think of it, one simple thing you can do that might improve your temps is to turn around just the rear 120, so it acts as an intake. This should improve overall airflow by better balancing intake and exhaust flow.
Edited by subtec - 6/19/11 at 7:57am