[Yetiman]

A wider gap (bigger spark) generally will give more complete combustion and easier starting, better low RPM operation.

If you start going wide, you have to make sure you have a powerfull enough ignition to keep up at higher RPM and bigger fuel loads.

Generally a bit bigger is better.

I have a small block running 10.5:1 with well ported heads and a 284/294 cam. I'm using an MSD capacitive discharge box with a Crane Cams Hall Effect unit in place of the points.
I run the engine to 6600 rpm regularly, and have settled into a .055" gap which seems to work well and solved fouling problems I had using smaller gaps with the original points setup.

When I went to the MSD/Crane and wider gap setup my fuel milage improved signifficantly (like 35% or better) than the setup the engine had when I bought it (.030" gap and points).

Much better driveability and power as well.