My apologies, I don't want to be a miserable sod here, but if you can, get your money back on these boots - the old Simms Guide boots were just fantastic, but the newer G3 Guide Boots are pants. Just had a refund on my second pair in fact, first pair failed when a stud came through the sole (make sure to put studs on the outer edges of the boots, not in the middle), and then the eyelets rotted out pretty quickly on the second pair. Simms have changed something and the eyelets no longer stand up to saltwater like they used to - they are still as good as new on my old battered Guide boots. I have asked Simms Europe and USA about this and been fobbed off with a load of rubbish.
Sorry, you don't want to hear this, but it bugs the hell out of me how Simms seem to have gone downhill with some of their gear. Vapor boots failed on me inside three weeks before I changed them for the newer G3 Guide Boots which have been refunded as I said. A pair of their G3 waders, whilst being the most comfortable breathables I have ever worn, have also been the leakiest.
And as for Simms studs, never come across any worse, save for some Goat Head spikes I once tried. Those star shaped Simms studs wore down flat on me in under a week on an Irish trip, plus half of them fell out of a pair of Rivershed boots - annoyingly the best wading boots I have ever used and Simms go and discontinue them. The studs were replaced a few years ago and I still have the (new) box of them sitting in my office because I see no point in using them. A good waste of money.
The joys of wading boots...........
As for studs, Orvis PosiGrip. Simple.