Gas, a few things to keep in mind. the 27.2 is a 34mm bore with 2mm crank. the 2mm will lose a tad bit of top rpm from the longer crank. the 28.5 should be using the 28mm stock stroke crank. thus a bit more top rpm.
now on the reed. is it a Reed Cage or a Reed Case? who built it for you or did you build it? what reed porting was done? Does it have the 5th transfer port?
when running a reed setup, they need to have pretty different porting done to work as they should, so the porting for the reed directly effect the motors performance.
and where are you loosing at? take off, topend? power out of a corner?
and lastly how much fuel has been run thru them? if your buddy has 4 gallons thru his, and you ve only got 2 tanks thru yours, that too can effect the performance. a new motor takes a few tanks (3-5) to fully wear in and loosen up.
Pipe choice is a HUGE effect on how the motors run. so what pipes do you each have installed? and finally what carb and how is the tune on each?