In my crawlers, I have no issue running a battery with a bit higher IR as long as it's even across cells. I'm not so worried about "punch" with those though as they seldom see more than 3/4 throttle.
The Vorteks once they are seeing above about 8 for IR they will start sagging and trip LVC...
What rig are you running it in?
In my Vorteks the LVC will kick in under heavy throttle around 3.8v per cell. On my Crawler it will run down to 3.5 no issue.