There is a good post on here about GT's with many guys giving the pro's and con's. I think the majority of guys are happy with them.
I shoot them, and due to my own mistake had trouble getting them to tune. I shoot a '02 patriot at 70# and was trying to shoot the 5575's, I think they are just a bit underspined and am going to try again with some 7595's I aquired.
I think you would be hard pressed to find a more durable shaft.