The Hakouchu Custom is faster in a straight line, but if the runup is curved then the Double T Custom is better, because it's better at turning. However, the Hakouchu Custom isn't necessarily better than a Double T Custom. The Hakouchu Custom is far better at low/medium bumps, but the Double T Custom can wheelie much more easily (which gives you more time to build speed before a bump), grind more easily, and it's a better all-around bike.
But, if you have TBoGT, you should just use the Vader. It's just as fast as a Double T Custom, it's easier to handle, it's amazing. The Double T Custom is a longer bike (so it can grind better than the Vader), and the Hakouchu Custom is lower down (so it can do really high bumps), but the Vader is better at everything else. And also, if you can hold a wheelie with the Vader, you can exceed the speed limit of the bike (just like doing a RAD in VC/SA). The Vader is usually limited to 185-190km/h, but you can get up to as much as 220km/h by doing a wheelie.
