It's generally acknowledged that the 21 is a faster bike as it's less restricted, and those restrictions are easier to remove. However, that's for the road, and will the full race prep done I guess the 28 won't be far behind.
What power are you getting from the 28?
Have you modded the suspension?
Have you lightened it?
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball