what if you ran a hotter plug? would you get a better burn?

If the only thing you did was change to plugs with a higher heat range, probably not. More voltage to the plug, optimal quench area, sufficient turbulence of the air/fuel mixture, grade of gasoline, timing, not running too rich or too lean, etc... all are part of a "better burn".

 

My experience with Bosh P4's in 2003 are bad. The plugs were wet with fuel when I removed them. I had a good A/F and I had very good voltage to my plugs. I learned of NGK V-Power plugs and used them spring 2004, I will never use anything else. I started with Tr-55's as they are stock heat range, after a PCM tune with lots of Timing advancement, I switched to TR-6's gapped .070 and love them. -Tim

 

Another vote for using what the application calls for. If copper plugs were OEM, stick with them. Plat doesnt conduct as well as (annealed) copper, so copper has the performance edge [of the two]. Copper will suffer quicker gap erosion, but if the plugs arent too hard to swap, it is of little matter.

Good luck.