2.5" or 3" exhaust?

I'm at kind of a road block and need your input guys.

Getting ready to do the exhaust on my project truck ('81 F100 w/460) and need a little advise. Currently the engine is a '77 460 out of a LTD. Updates are: Weiand Stealth intake, Cam timing straight up, Edelbrock 800 carb, D5TE exhaust manifolds. Now, in the future, the truck is getting a fresh engine (this one is just to hold me over for the build without emptying my wallet completely). It will consist of a pair of C8VE heads, 2.19 and 1.76 valves, between 9.5 and 10:1 compression (has to run on premium or less pump gas), truck rods, same intake, carb, exhaust manifolds and such.

The manifolds will accept 2.5" pipe, but I don't have anything to do that size. I have all kinds of 3" stainless tubing (polished inside and out), mandrel bends, 3" stainless mufflers. I can always pick up all the 2.5" tubing I need if that's the best route.

Which is going to be the better tubing size for BOTH engines?
Is the 2.5" going to flow enough?
If you think I should run the 3", how far away from the manifolds should I put the adapters to go from 2.5 to 3"?

This is only a street truck and will probably never see over 5500 rpms, so I'm not worried about really revving it.

Any help would be greatly appreciated.

Dave

Go big or go home. LOL. Step it up where the headers you will eventually use come to an end.  

Spend the money on some headers and use the 3" tube, its well worth the upgrade over manifolds.

Those were the responses I kind of expected.  Thanks for the push in the right direction. Save money on the tubing, build some headers.

Thanks guys!