i m having the same choice, complicated by the fact that i m aslo considering trf 417.
however the big doubt is about tc6/t3...
i m from italy, and here the situation until last few weeks was the following:
in my track if there were 10 people the cars would have been:
the point is that since 2 or 3 weeks almost half xray drivers switched to asso,
so that now the same 10 drivers are:
guys that changed are VERY happy, according to theme the car is easy, have more steering than almost every machine else, is strong and with a complete new design have a perfect balance.
however the car, coming out of the box, is made for high grip surface, so that if you are running mid/low grip hasphalt you need to change some small details.
furthermore you have to consider that here in italy xray parts are the most popular BUT even the most exensive, meanwhile asso parts are not so difficult to find and cost even half price.
plus we have to consider that car popularity is a key factor in the choise, i would not have chose a tc5 beause no one was driving one for miles, so would have been very difficult reach any help on the track, just talking on the car, etc..
with the tc6 is quite different, is becoming very common and, even if i was not a fan (i drive mi4lp race) , i can tell you that xray drivers are now happy enough to not regret their choise...
finally if you consider that tc6 cost here almost 100 euros less that t3...you can easly understand that i m very close to the choise!
hope this help!