Within 200 rpm though? That's my point. I suspect most clutch builders are setting their clutches up based on experience.
Yes, a clutch can be set using a dyno, but I seriously doubt that's how everyone is doing every individual clutch.
Then consider that clutches need some break-in time to wear and bed in the discs. During this break-in, the clutch changes engagement rpm (often by 200 rpm.)
With rolling starts and the flat torque curve of ohv engines used in karting today....I am not convinced that the OP's problem is engaging the clutch at 4000 rpm vs his peak torque (which is very likely within 200 rpm of that.)
Dynoing shocks is a whole 'nuther adventure. Testing at 2", 3" 5", etc for velocity/acceleration and pounds of compression/rebound to customize shocks has become a whole industry of its own. When I first got my shock dyno, I just wanted to know if the shock I was testing was "good" or flat. Were they as advertised, or somewhat different, and how different? What I learned was very eye opening.
When I stepped out of running the big car full time, I gave thought to getting into doing shocks for other teams (mostly sprint and dirt late model.) That would have been a great time to get in...now everyone and their brother-in-law has a shock dyno and most teams have ones mounted in their trailers that put mine to shame.