You should really be getting better temps. I have battled the last couple of months with two different cases. First one was completely sealed and, when I added 5th Hard drive, OS drive jumped to 52 degrees and windows ran a disk check every time. Its resolved now on Tuesday with a side fan blowing away from the disks and a slot blower on the floor of the case blowing under the lowest drive. CPU and MB were sorted by opening two lowest slot covers and adding Exhaust fan at the back. Did a ghetto mod on the front bezel to push air out.
First PC however is the complete opposite, when I added a back fan temps went up. Had a Zalman 9300AT on the CPU and made no difference with the back fan on. The case has 200mm side fan. Tried the whole front bottom fan blowing in thing and back top exhaust and did not work. So Slot cooler that made no difference in the second case dropped every component down 5degrees. Now have the 9900NT and suddenly my GPU is up from 65-69 idle back to 73 of last summer. aaaaaarrrrrrrgh. Slot cooler has no effect now for some reason. So took slot fan out and put in perforated cover on to make two perforated slots on the back bottom two. What do you know, GPU no change, OS HDD down from 38 to 33 idle and 35 under load. (NB have front fan blowing out now, go figure) So, I believe you can get up to just 10degrees over ambient but you need to try everything around your case.
940 Phenom II at 3300mhz
Cosair Dominator 2x2gig at 880mhz
M3N-HD/HDMI board
ASUS Top 9800gt at GPU 709, Mem 1058, Shader 1772
ODIN 585 Power
Zalman 120mm Front
200mm Side fan Inducting
Case two
AMD 3800+ OC 10%
M2N-MPV... not sure anymore
Asus 8600 stock
ODIN 470W power
One Open Back slot
80cm Fan Side of Drives (5 Stacked) tilted slightly up
Blower fan 32CFM on base of case
Cooler Master 80CM back fan
Cyclone Blower Mounted in CD Bezel topmost front
That's that.