With the Hayes mechanical discs there's two things you need to ensure to obtain the best brake performace.

First is that the fixed pad has to be REALLY close to the rotor. A little skim sound per rev is typically unavoidable when it's set right. To keep this right it requires fairly frequent adjustments so keep on top of it. The reason this is important is that if the pad is spaced back too far then a lot of your lever effort goes into flexing the rotor over until it pinches the fixed pad and then you STILL have to make the rotor form an "S" curve before you achieve the maximum pad to rotor contact needed for effective brake performance. So the closer it is, even if you have to live with a bit of skimming sound, the better your braking performance will be.

Second is the levers. Levers on these brakes makes a HUGE difference. The lever and caliper form a system and the system is only as strong as the matching of the components. I found that the optimum levers for these Hayes calipers as well as for the Avid mechanical BB series are the Avid Speedial levers. Screw the movable shuttle up until it's as close to the pivot as possible and your brake performace will take a huge leap upwards. In fact it woudl be fair to say that at that point they can match a lot of the cheaper hydro systems for performance if not for feel.

And if on top of these two things, which should really be done first, if you do go with an 8 inch on the front it'll just be that much better again. But first and foremost is that fixed pad adjustment. Learn to do it right and keep on top of it. Then do the other two things as time, money and desire hits.