Today our coach (collegiate club rowing) prescribed a 6k test with a rate cap of 22. I pulled a 23:17 with an average split of 1:56.4. The low rate cap put my quads out of commission for the rest of the day

My height is 5'10, weight 160 (incidentally I'm the smallest guy on the team; I did manage to beat two other rowers both taller and heavier).
I'd like to know, now that I have this baseline 6k split, how I should adjust for longer pieces (40 minutes and up, 10k, etc.). The neighborhood goal pace of 1:59 or so sounds good, but I haven't been able to locate any tables based on 6k splits (although I have seen the Wolverine Plan's 2k split tables).
Any advice would be appreciated. Thanks!
-W