I've got the Simms guide boots as well. Nice boot, and they'd better be for the ridiculous price!!!! I too came from felt, which I still have and use on occasion.
Mine also have star cleats, though the alumibite ones.
As a direct comparison between the Simms and studded felt, well, there is no comparison. Felt is hands-down better traction. Sure, rubber is better in mud and soil. But when fishing, even on the banks, 99% of my time is spent on rock, and for that other 1%, I never really struggled with any sole. Anything is fine in gravel and broken rock as well. It's the big boulders, flat or rounded, where you really notice the difference, and of course, that's where you really need the traction.
That said, the traction isn't terrible with the rubber. I'd call it "acceptable". Better than I feared, for sure. My only rubber soled experiences had been those cheapo rubber hippers, which are downright deadly IMO. These Simms are far superior to that.
As for longevity, doesn't look good. After only a dozen or so outings the soles are beginning to flatten out a bit, just like hiking boots with softer rubber do. I still have a lot of tread left, but the fact that it's even noticable this soon isn't good. That's always a trade-off, I guess. Hard rubber lasts a long time, but offers poor traction. Softer rubbers offer better traction, but wear down quicker.
Perhaps if going the rubber route, you just gotta look at them as expendable equipment. Like waders, something that will last 2-4 years and get replaced. And if that's the conclusion I come to, for the next pair, I probably won't spend north of $100.