tbh, OCing isn't a must, I streamed on 3.3 on an i5 with TF2 no problems, with an FPS config of course I'd get around 250 fps stable in 6v6 and around 150 on pubs/highlander.
TF2 is a bit of a mixed bag in terms of every ones performance, you might have that rig and find no issues streaming at all with an fps config, yet others might stutter loads with a similar set up.
My specs: Intel i5-2500K @ 4.1 Ghz
16GB RAM
Asus HD 7950 DirectCU II TOP V2 3072MB GDDR5
1x 500 GB HDD
1x 250 GB SSD
The OC boosted FPS by 150, the GPU had none :D
imo your rig should be fine to run TF2 and stream.