Mad, this is opinion and opinion only...

Under normal driving conditions, I wouldn't expect much difference. However when in high R's, larger gap helps keep the timing more stable. If you have a powerfull enough ignition system that can thow some spark, gap 'em in the 40's. If you're using stock coil (or HEI), you may not see the R's because those coils are weak and do not saturate appropriately the higher you go (they're good to about 7000 max). And yes, changing your fuel/air intake does make a difference. You need to be able to burn that stuff. A weak spark may not efficiently burn all of the fuel, thus causing you to have to idle a little higher or run more advance...or hotter plugs.

So, about the timing issue, see above about pumping up that spark. Change out your coil if you suspect the plugs are weak. Some other things to consider is have you changed the cam? If so, the lumpy "poketa pokata poketa" type cams generally have a large lobe overlap. This will cause a lot of reversion (exhaust to intake backpressure), thus giving you a contaminated fuel charge. That leads to bad combustion at low RPM's and bad gas mileage when driving in the low R's on the street. This could also cause you to advance the distributor so it will idle.

Take it for what it's worth...

tj