GMX aren't pure copper which may account for the less amount of fouling you've seen with them Desert Dog. I'd agree that the GMX does need a bit more speed than the TTSX. I find it more like the TSX for expansion. My 7mm and Vanessa'a 30-06 are both well sub MOA with Superformance and my .338 is right at MOA. We've shot animals out to 500 yards with all of them and Vanessa tipped an ostrich over at 622 with a 139-grain GMX in the 7mm using Superformance. On our latest trip I took a Barbary sheep at 500 yards with the 185 GMX out of the 338. I've definitely seen no accuracy issues with Superformance. The only rifle that didn't like it was the 6.5 Creedmoor.