OK just some insight on the subject. The TAG class is popular these days as is the stock moto platform. The speeds are close, slight advantage to the shifter on some tracks, TAG on others.
Now when it comes down to cost there should be a substantial savings in running the Moto package. Mainly due to the lower revving motor, 12500 Vs. 17000 rpm. Chain size 219 Vs. 428. The TAG's put out 26-28HP Vs. the Moto's 33HP. That is why the TAG karts go through chains every other race, not to mention sprockets. The Moto chain will last a whole season and so will the sprockets. One piston and two rings on the moto per season and every other weekend for TAG. On the topic of rebuilds. Stock Moto crank 2 seasons, TAG 1/2 season. Stock moto crank $150, TAG $400. TAG clutch one season (maybe), Moto clutch...mine is going on 6 years!
If we are going to try and put together another step up the performance ladder It is my opinion the Stock moto platform should be the one to pursue. Just my opinion and your welcome to tell us yours!