Problems at high speeds.

[Fazerider]

I doubt balancing the carbs will have any effect at those revs/throttle openings… if you've difficulty starting/getting a good idle or it's snatchy at low speed it'll help there.
It's much more likely to be one or more slides getting jammed especially if you're snapping the throttle fully open. Does it accelerate OK if you feed the power in gently?
Another possibility is that aftermarket downpipes aren't a totally accurate match for the OEM ones. Some have the link pipes between cylinders 1&2 and 3&4, but most don't match the diameter of the bit after the collector to what Yamaha tuned the intakes,carbs and airbox for. The OEM one is quite constricted at that point some have found sleeving down aftermarket downpipes to about 35mm internal diameter improves fuelling in the middle of the rev range.