If you can't afford a road bike for now, it's okay i guess, from the terrain over which you cycle on. A mtb with slicks goes faster than one w/o, but gives you more grip on the sands if you're on knobblies. I don't know what your bike setup is like, if you're on standard Deore, with M540 wheelset or one with XTR hubs, you'll be some of the faster mtb around. If you like, can even use a rigid fork to shred some weight off your bike.