PCI Slot Coolers - Heat management and Overclocking, a discussion

Alright so,
Currently in my 4 year old computer I have a 7800GTX OC, Athlon X2 64 2.0GHz and a 650W PSU 120mm fan for back exhaust, 80mm fan for intake and a stock heatsink/fan for the CPU. Cool N Quiet disabled.

As of now, everything runs a bit hot.. but with no noticible side effects (no crashes or artifacts)
While writing this:
CPU: 35c,
Core1: 50c,
Core2: 44c,
GPU: 54c,
Mobo: 35c

During a test of running COD4 my GPU got up to 100c one time.. don't remember what caused it but that caused my now wanting to manage the heat better in my case (ASUS Vento (big red steel thing))
At load the GPU tops around 80c.

Right now I have a 8800GT and a PCI Slot cooler en route to my house via UPS ground.
I believe that the 7800GTX is overheating due to it's age and could just benefit from me taking off the heatsink, dusting and reapplying some after market thermal paste.

I'm hoping to see a noticable decrease in my tempreature overall by exchanging the GPU and adding a PCI cooler.

Now..
With my AMD X2 64 Socket 939 2.0GHz and 400MHz DDR2 kind of showing it's age I'm wanting to start overclocking everything. Various sites have shown my Manchester chip and Foxconn motherboard as both yielding very good OC results but with my heat level where they are now I'm reluctant to begin the process.

So finally the point of all of this long explainations:

Would a PCI Slot cooler a few slots below my 8800GT as well as an additional PCI Slot cooler ABOVE the GPU in a PCIe x1 slot to help dissipate the CPUs temp.. along with a new layer of AC5 Thermal Paste on a new AC Heatsink (alluminum, not copper) or would that just be overkill.

Would the two PCI coolers be helpful? Should I just say no to the PCIe x1 slot cooler and get new thermal paste and heatsink?

What temps should I try to strive to before beginning the overclock process?

Any input on my thoughts are appreciated.

Items referenced:
case: http://www.newegg.com/Product/Product.aspx?Item=N82E16811173003
pci cooler: http://www.newegg.com/Product/Product.aspx?Item=N82E16835888309
paste: http://www.newegg.com/Product/Product.aspx?Item=N82E16835100007
heatsink: http://www.newegg.com/Product/Product.aspx?Item=N82E16835186010