Depends on the cab IR, and the amp model in use. On the Atomic stuff, with stock cabs, they recommend starting at around 8K and then rolling down from there as needed.
I also have a Jay Mitchell post where he gave a more surgical method of removing it with a parametric EQ block. I might be able to find and copy it here. It's from the Atomic forum.
Thanks for the offer, no need for bringing in the Atomic. I prefer Choptones mostly, and these allow hi & low cut and gain addition or attenuation.
8 KHz seemed like a decent number to begin with, so I'll try that and see where it takes me.
Regards the parametric EQ, most of my effects blocks are occupied regards my high-gain rigs, and I've already learned that it's not wise to run high-gain rigs with too many effects. The problem is, as it stands now, additional effects just muddies up an otherwise clean signal, and being able to clean up with lower volumes is preferable than running high gain amps full up all the time.
The IR cab hi-cuts will be enough for solving my fizzy harshness problem, theoretically. Will report back later this afternoon.
P.S. Thanks for the insight regards the parametric EQ. My personal expertise using parametric EQs isn't that developed yet, so I'll need to step away from trying that for now.
As an afterthought, it might be possible for me to post a question on the HeadRush Forum about this topic. There might be some posts there already that might have addressed this, as well.