I've never heard of an MT-500, and there is no mention of it on the Raleigh page. I can find no mention of it anywhere. Raleigh tends to give good components (deraileurs, brake, shifters) at the cost of a heavy frame and a cheap fork. I suspect its a RS Judy TT or a RST fork. They're anything but the best, but they do the job if you're looking for an affordable bike. The frame, like I said, is heavy, but its tough as nails.
4900 is a similar story, cheap fork, cheap components (alivo / and some deore), its a pretty light frame though.
If you can find yourself a used 02' stumpy I think you'd be pretty happy with it. The Duke is a great fork, and the M4 frame is what they're still using today.