As for the TC6.1, I drove one in 21.5 for a bit of fun a few weeks back and loved it, however there have been a few that have tried it in stock and hated it.
Since moving to mod i think it has allot to do chassis flex, the 6.1 is a little stiffer, and lacks a little on power steering and rear grip because of it, ( wow Ari's wisdom was right
)
Its fine for 21.5 as its very underpowered, and probably makes it a little easier to drive.
When i get back from real racing in a few weeks, im going to give the 6.1WC chassis that has been collecting dust in my pit bag, and a flexi top deck a try to see if that helps in Mod
Beth.