Actually Centaur is probably the only OP tank the Brits have in this patch.
The new Centaur sure is the gem of T3, pretty much required at all times.
The Croc I do get now and then as it does a decent job at protecting your AT gun and VP's from pesky blobs over running your position. Just like the AVRE it is NOT a spearhead unit, rather a inf mop up unit that comes in from behind.
I can't rightly comment on whether its overpriced as I don't play smaller game modes.
You can only risk getting it when you have AT department fully covered, making it more a covering all bases unit, than a game changer.
The Comet is an overpriced tin can, basking in the light of its former glory days and best avoided in team games.
I'm finding the Churchill VII a more reliable option for late game as it serves the distinct role of leading the charge, tanking shots, and believe it or not, effective flanking.