Hey guys,
I'm no expert, especially when it comes to the kind of heat you guys have to deal with, but I know that Woody (azgn) has commented on more than one occasion that in back to back testing they noticed almost no difference between a V4 and V4R, and only a slight difference between the V4 and V2 front mount in the Arizona heat on a low 11 second car. My point? you can probably save yourself some $$ by going with the regular V4 instead of the V4R. Unless of course you are planning on building a mid-low 10 second all out racecar, but then why not go with a front mount right? The V4 has been in the 10.60's so far. I personally know of 2 guys out here that are going 10.9's with the V4 and they have more left.
Just some food for thought. Hope it helps some.
Later,
Clayton