Well, if you Really want a TQ and don't wanna wait for the full TQ kit to be released, just upgrade the XB8 you have now.
If you think that the TQ upgrades will improve the handling of your car on the track that you race on, then yes, upgrade your XB8, or get the TQ when it is available.
If your car is running great the way it is, and you are happy with your set-up, stick with what you have.
Either way, you'll have a great car.
FRom what i've been hearing, the TQ may be very close in pricing to the XB8. But i don't know for sure, so i don't know what is the cheapest way to go. I'm assuming it's cheaper to buy a TQ, then to have a XB8, and buy all the upgrades for it.
Hope that helps.