Will this change once I add add another stick of DDR and start running in dual channel mode?
Your CPU won't run a single bit faster, but the access to data in the memory should be a lot faster, so yes, the overall system perfomance will increase.
Although dual channel memory is a nice technique, you should not expect to much from it. It does good to your system performance, but your memory perfomance doesn't increase with a 100%. Even not with 50%. It kind of depends on the applications you are running, but a 10% gain is more than optimistic enough.
I noticed when I bumped up the FSB 5% . Everything was okay temp wise but the computer seemed less responsive??
This should not be happening. The only thing I can think of that causes this, is that your BIOS didn't lock the PCI and AGP bus at x33Mhz clockspeed, resulting in a component that can't handle the too high clockspeed. See if your BIOS has a function to lock the AGP/PCI bus clockspeed!