I've been a long time Wipeout tragic and have always used the D-Pad as it's what I've been used to.
I've tried using the sticks but find 1] my thumb tends to slip off the top of the domed topped sticks, this effects lots of games 2] And specifically to Wipeout, I can't do the quick twitch of the stick side to side to do a barrel roll using the stick...it might be because the distance difference....anyway..fail on my part doing that.
Doing Barrel Rolls using the D-Pad isn't much better for me; I can do them pretty well for around 30 minutes then it all falls to pieces as my thumb gets worn out.

Anyway, I've been messing around with polymer clay of late [anybody that doesn't know about this stuff, it's a cheap easy to get plastic clay that you can mould to any shape you want, you then put in a household oven and bake/cure for 30 minutes at 150C so it sets hard].

I've been thinking about making some custom replacement D-Pad's/sticks and maybe even triggers that would 1]Stop my thumb slipping off a stick 2] Designing a D-Pad that would make barrel rolling on Wipeout HD a LOT easier and not a thumb killer.
The more I think about it, with the addition of magnetic or screw in jewellery clasps, you could make a set of adjustable controller sticks that could have a variety of different head portions that you could easily swap over so they might suit different games.
I use KATO brand Polymer Clay by the way, as it's the strongest and resists chipping, I doubt the other brands of clay are really up to the task for this usage.

Anybody else tried this sort of thing?