Not to say your suggestion is bad, but it's not very good. I think they should rather use a base model seeding, therefore if you ride say A batch road races you should be seeded in an equivalent batch on the mtb races. People will be sorted in batches of equal fitness level. Most of the xc mtb races here are anyway fairly non technical. I had a slight mechanical issue at the race start, forcing me to be the very last 60km rider to go. My avg speed was around 24kmph when we hit the singletrack with the lynnwood cyclery boards. From there due to slow riders and people who brake for no reason it started dropping, by the time we hit the final 10km i had dropped 3kmph on average speed. So us being impatient is understandable IF the organisers put (i'm guessing) 500 people on a course with 90% singletrack AND as you said with the 40km and 60km ending together. Also I think they should let the 40k racing snakes go before the 60k batch with a gap of about 5min, we'll never catch them and then we won't have some little twit just come flying past on the dodgiest of dodgy places.
