First, your bike has stock gearing so it won't go any faster then STOCK. It will get there quicker, but the MPH will be the same unless you are carrying a little bit more RPM.
Second, the T5's aren't for stock motors. They do a pretty decent job of complimenting fairly modded motors. They are probably plenty for your set up, unless you want an inframe drag pipe.
Third, fuel type is dictated by the motors needs. Putting race fuel in a motor that doesn't need it will hurt performance. You hear guys say they run it thinking it gives more performance but in reality a lot of guys running it aren't actually getting a full combustion. Race fuel is for motors with higher compression and additional timing. What kind of timing are you running and what is the compression ratio? This could also be part of the dead spot on top.