I think the off the peg has a grasstrack style geometry, so slightly relaxed angles, more fork rake than you might expect and greater tyre clearances. Also a very high BB for cornering on a flat track, and the fork is drilled for a brake. These characteristics obviously transfer well for street FG riding, but not so great on a banked velodrome. Shell out the extra 55 quid and go custom, enjoy a bike built exactly the way you want it.