I have a KLX 400 Factory DS (re-geared for +low-end)and I can keep up with my buddy in very tight, quick riding on his land where we have a bit of a track through trees. He is on a CR 85! Of course that is a quick bike and he is about 41 yrs old and maybe 5 feet 1 inches in size so the 85 is about right for him. He has a Harley BS and other bikes as well.
Also I have over 30 yrs experience riding and he is of similar tenure.