Roller
I agree, there do seem to be various opinions on how much overexposure to dial in, but the main reason I chose 4 stops was due to a very useful thread I found on here - Rollei IR400S - it's not HIE, but WOW - in which photos were posted of shots taken with that film at various settings, and to me, the 4 stops over example looked the best.
I also agree about bracketing shots, it's just that I've got quite a few subjects I'm going to shoot and wouldn't be able to get them all done if I bracketed 3 shots on each one. I might do it on just one of the subjects though.