Id say that up to 600hp an 833 18sp will hold up just fine. More with a good race clutch.
Biggest downside on the 833 is the lack of different ratios.
Im not sure if liberty still have the 2.94 gear sets.
I have a gforce in one of my cars and like it alot but they are not indestructible and when they break its about twice the cost to repair vs the 833.
So if you are around 600hp and want a bolt in deal the 833 will do the job.
But without a good race clutch i cant see it beeing that fast.
My alltime biggest et improver was a softlok clutch. From 1.47 60 to 1.32 no other changes.