I have no need to over clock my GTX 480, But have a ?

In my GPU over clocking programs (I have 2 to check one against the other for accuracy) I see that the core is locked, but the shader and memory can both be over clocked.

Can anyone tell me why it's like this?

And if I ever need to over clock can I see any significant gain by OC'ng the shader and memory only?

I am locked at 60FPS in FSX though so I don't really think I'll do anything other than run my fan at 70% while in FSX like I've been doing.

And to quell any rumors about how hot the GTX 480 runs, the fan on it is at 44% at default I think when not gaming and it is in the 40's C as far as regular temps.

Before I start FSX I set the fan on the card to 70% and I usually hover around 65 C while using FSX, the hottest I've seen is 72 C so far.

So those folks complaining about temps around 90C don't have adequate cooling or something.