For me, GP4000s ride a little nicer than the Gatorskins (which ride a little harsh for me). As I understand it (and I could be wrong), the GP4000s have the same kevlar band as the Gatorskins, but, unlike the Gatorskin, it does not extend up into the sidewall of the tire. Thus, if you kick up a lot of sharp stuff, the Gatorskin would be more flat protective. I've had good luck with the GP4000s.

Anothter tire I've ridden a bit is the Panaracer Duro. Getting it on the rims the first time is a real beast, but after that not so bad. They are a tough road tire and they ride somewhere in between the Gatorskin and the GP4000. I was running the Duros and DH the Gatorskins in Tucson in spring (where there is more glass and goatheads on the pavement than anywhere else). DH put glass through new Gatorskins; my Duros got cuts, but none of them did more than just nick the tread.