OC CPU or second GPU?

k, so i got my hands on a Gateway FX system... but i am stuck on a crossroad on how to speed it up...
Here are quick specs... (not all is stock)

CPU: E6600 running stock @ 2.4 Ghz
RAM: 4 Gigz Ocz Gold 667
GPU: HD 4850 512 mb
PSU: 700W Delta http://support.gateway.com/s/POWER [...] 9Rnv.shtml

Now, first i was thinking it would be just easy to drop in another 4850 since its a crossfire mobo... but then i was thinking it will probably get quickly bottled by the 2.4 Ghz

So, OC the CPU... and then maby later get another 4850.... can't be that hard right?

Well here is the problem with that... the mobo is a BTX setup .... aha.... but thats fine i could still put in a good heatsink and OC... the stock heatsink is just a huge hunk aluminum, like huge, with fins, and the front 120mm feeds air to it using a duct. I decided to do some research on the mobo, make sure no more surprises....then i found that the CPU is rotated, so its more like a diamond on the mobo then a square... but the holes for the heatsink are positioned correctly..... here are some pictures

http://img193.imageshack.us/img193/6223/1130081855.jpg

http://img132.imageshack.us/img132/7402/1130081854.jpg

http://skyline-eng.com/images/products/Big%20Arm.jpg <-mobo

http://support.gateway.com/s/CASES [...] 8Rmv.shtml <- heatsink stock

So an alternate cooling solution i came up was this... replace the front and back 120mm with the 120mm from newegg with the greatest airflow, and then get an 80mm fan (there is one on newegg that is like 6000RPM) and put it right on the side of the heatsink (right in the duct, so it blows air from the front fan over the cpu sink)

So...should i not worry bout the bottleneck and get 4850.... or do the new cooling solution and OC... or do u have something better in mind?

not this one, they would OC it themselves from some $$$, but raising the FSB is funtional...