The True Fit is probably about 3" taller in the shell than the MR65. That's a guess. I measured the shell of the TF at 27" (or was it 28"? 27" I think). DD is about 40" tall and has several inches above her head in the TF (see my sig pic) but when I tried her at BRU in the MR65 yesterday, she was at the top. However, it was NOT installed when I tried it and it had the infant insert, so my guess is that she'd have about an inch left in that seat.
If height is your concern, I'd go for the True Fit, personally. It has the tallest shell of any convertible on the market. It could take your child a while to gain 4lbs. Of course, growth spurts can't accurately be predicted, so....? I don't know. Sorry, I may not have helped as much as I was trying to.