I think we can finally kiss that old "theory goodbye". I'm glad this came up again b/c I actually took the time to research it more. There used to be a 203-taboo. Mfgr's wouldn't warranty issues related to this. There were "rumors" of sheering off QR's and wrenching hubs out of dropouts. I've read a crapload this morning about people all over the world using 203's on QR forks with no problems. The main "disclaimer" they offered was "Tighten your QR!" Apparently some have come loose?

Regarding you locking up your wheel with a 6" rotor...this sorta comes down to people in Lee's Summit thinking mountain biking is riding a 29'er on smooth trails. For me...mountain biking is different...but that's all that they see or come in contact with. Myself...weighing about 50lbs more than you...I can't lock up my front wheel with a 6" rotor. I can do it with a 7 or 8 though. I figure since I weigh more, I've got more weight to stop but more traction to do it b/c there's 205lbs of weight pushing my tires into the ground.

By Guy Kesteven, WMB & MBUK
Buyer's Guide to disc brakes

Buyer's Guide to disc brakes (Russell Burton)

Hydraulic disc brakes are now coming as standard on most mountain bikes, but what should you be looking for when it comes to shopping for your ideal stoppers? This guide explains the basics, and the Jargon Buster below will help you get to grips with the terminology.
Disc/rotor

Power varies with each calliper and its pad surface/leverage, but the biggest difference is in disc (or rotor in the US) size. The bigger the disc, the more leverage your brake has on the wheel and the faster it can stop it. Each 20mm increase in size roughly equates to a 20 percent increase in power.



Fox:
Disc brakes with 160 – 203 mm rotors can be used on FOX 32MM forks. Do not use rotors larger than 203 mm.

The 2012 Marzocchi 44 LR website:
» 6" PM D-BRAKE (MAX 203mm)

White Bro's "Rock Solid" carbon rigid:
( *Max Rotor Size 185mm or may void warranty)

Rockshox Tora:
Maximum Rotor Size 210mm