my understanding is that the lag is because the software goes through and checks each enhancement on each tree individually to see if they have been acquired, and then adds the bonuses accordingly, one at a time, resulting in lag.
Why not add a 'reaper tab' to the character sheet that would be updated through that same process, but it could be done when the reaper tree is updated, instead of each time a quest is entered, then instead of a bunch of queries at the beginning of a reaper quest, it would just add the precalculated bonuses on the reaper tab. Seems like an easy fix, plus a nice place to view your total reaper bonsues.