That "Extreme" property is ONLY valid for the cartridge(perhaps family) that it was built for. Varget works well in the 308, but NOT in the 223. Is it a BAD choice for the 223? No, but the praise of insensitivity does not exist in that application.
Yes, if you go slow nothing will ever be an issue.
Using my IR temp gun, Between Varget and 748(in my 308) the 748 heats things up noticeably slower(shooting same MV).
When I get settled on a Rock chuck hive, it is completely normal to shoot round after round. Obviously that doesn't mean that you HAVE to do it. But Personally, If I can get 5 more rounds down range before a required rest, I'm all for it.