What are you buying it for? If VTA, I'd just stick with the TC3 - it won't be that huge of a difference and more people run them than the FT TC4. The FT TC3 includes some titanium goodies and carbon-composite plastics - nothing huge.
If for regular touring, look at one of the current belt-driven cars - huge difference between them and the old TC3/TC4.
"the big secret is to keep practicing and never get discouraged when taking a good beating on the track" - Paul L