[Closed] Disc Rotors

if you're average weight then go for 180 on the front, go biggerer if you feel it necessary. bear in mind bigger discs are more easily damaged.
you don't need hayes specific adaptors or rotors.
mtb-direct do rotors which are fine ( i have one of their imperial 180 rotors on the front of one of my bikes running hayes nines ) and they're cheap too.
you may want to consider some organic pads for the alps as they better deal with heat. i just bought some from discobrakes.com for a good price, though i cannot testify to performance.
HTH.

You also need to consider if your frame and fork can take a 203mm rotor. Having a bigger disc may mean that the disc is to large and the frame hasn't allowed the room so it may rub on the disc. The other issue is that the braking forces on a 203mm rotor could be to much for your disc mount and cause damage to the frame or forks.

Most people run 203 / 180 up front and 180 / 160 on the back.

Thanks for comments. Unfortunately I am 16stone so will probably go for 203 front and 180 rear - I have a Meta 5 with RS Pikes - should be OK

Your choice is probably OK, but I've found that big rotors on the back aren't really much cop, if you can lock the wheel with a 160, 180 isn't going to do anything much more. Save the pennies for beer...

I've just got back from the alps with 180/160 and wished i had at least 200/180. my brakes got murdered out there. (hope m4's) didn't notice that much fading but yeouch the heat that got produced was crazy. I've heard my brakes squeal once or twice due to heat here in the UK but over there it was a regular occurrence.

Rotor size is not about being able to lock the wheel, its about heat dissipation.
Go for the biggest that will fit 203/180 (floating will be better)
If you are overbraked - who cares, if you are underbraked then the Alps is not the place to find out!