I've used Simms studded felt boots with good result, but they've worn out after a year of hard use (I walk miles over difficult rock). Another major advantage to wading boots is the better ankle support which greatly improves your balance and lets you move much faster (increasing your fishing time). Now if they just had something for my knees.........
By the way, Simms sells the screw in carbide snowmobile studs....you can get them through most flyfishing outlets........try Kaufmanns Streamborn.....(here's a link if that is OK)
http://www.kaufmannsstreamborn.com/C.../SIMSTUDSOO14/