is it safe to run this setup?
 

3905 emaxx with mmm/7xl with a 2s 25/50c lipo and a 3s 12/25c for just a few speed passes.
my buddy is here with his vxl slash, and im very tempted to use his 3s lipo to try and see how my emaxx will perform.
will just a few speed passes ruin our lipos or my mmm?

Take a video camera so we can see the flames... (i think you get teh idea)

LOL dang you serious? not even just a few speed passes? so whats gonna go up in smoke...the lipos are the mmm....or the 7xl? hhah

Yes serious... All or a combination of Motor, Lipos and MMM

Whew!! am i glad i asked on here first, because i was seriously gonna just try it because i honestly didnt think a few speed passes was gonna hurt anything. but i said what the heck, i should just ask RCM since they usually respond quick anyways. THANKS!!
But, if his 3s lipos were 25/50 c, then i should be able to do a few passes right?

Much better but you still risk trashing the motor which can take out your ESC and hence lipos.

Also be aware that even though same C / mah they will be "unmatched" so wouldn't run more than a few passes.

unmatched meaning different company or different number of cycles or ?

Yes. Both are crucial factors That would change the internal resistance of the pack causing, one to drain more then the other.. which would make one pack drain faster then the other.