Bit of an update on this...
The M4's were doing my head in, they just didn't really want to work, especially in the wet so I decided to cut my loses. They'll be going on eBay this week and have been replaced by a set I'd Deore brakes from CRC.
They turned up on Thursday and weren't dodgy OE jobbies...they actually came in a box! Can't fault them for forty quid an end.
The good news is that because the use the older style pads, they fit onto the old M4 rotors which I have had to keep due to running old school Bulbs with a five bolt pattern. The disc spiders caused me some real headaches, especially on the rear. The rear adapter as had to be filed down massively to stop it catching on the disc bolts. I also had to swap the old style disc bolts for newer torx head ones to improve clearance. The rear calliper has also ad to be spaced to fit a 165mm disc because the adapter is or a 160mm rotor.
The front was easier because only the very bottom of the adapter had to be filed and its an Avid 185 so fits my bigger rotor perfectly. I also ditched the stock hoses for some white ones because I'm a tart!
Overall I'm pretty damn happy. For he money they seem unbelievable, just need some better weather to go and get them bedded in.
I also need to find the source of an annoying creak, can't decided if its coming from the bottom bracket or from the cassette. I'll do some fiddling this week.