I thought that shudder at speed meant warped discs.
I had this on the back of my S1 several years back and replaced the discs. Warping occurs more easily on rears because handbrake can be put on when discs are hot and this can apparently cause an issue.
Upgrade, why? Haven't found any shortage of braking on my Aero 8, including some agressive driving down Swiss Alp passes.
Assuming you have the thickness, skimming is definitely the way to go, and discs are fairly easily removed.
Cheers
