RE: 85 Combat slide stops.
Yes, for those who are unfamiliar with the 85C, they are different--because they are for an ambidextrous model. The far end of the stop has a smaller, slotted end to fit into the lever on the other side of the frame.
Slide stop breaks are very rare in CZs, but they do happen. When they happen regularly, it seems to be a function of slightly out-of-spec openings in the frame. Yours is hardly happening regularly.
(Some Witness and Tanfoglio guns used in IPSC, back when they were the "hot" gun there, were known to have slide stop breaks at 20K - 25K rounds; that's not exactly the same slide stop, but it is similar -- and some are interchangeable with CZs. I've never heard of a source for different slide stops, and I'm not sure brittleness is the issue.)
Playing at the range one day, years back, swapping slides between guns, I mistakenly -- didn't realize I was doing it -- installed my 85 Combat slide stop [which is the same as the 85B slide stop] in my [non-ambi] Compact, and it broke after about three or four rounds fired. Duh. The far end wasn't properly supported, and allowed the stop to set at a slight angle, so that the barrel wasn't engaging it flushly. That had the effect of transferring the force of the recoil or return into a smaller area on the slide stop. I've seen two breaks: the 85 C break was near the far end, and I've seen another standard 75B slide stop break -- not mine -- nealy in the middle.
Mike Eagleshield, head gunsmith at CZ, recommends a heavier recoil spring to minimize breakage, but I've always felt the cure was as bad as the disease -- as a heavier recoil spring causes the slide to slam forward with much greater speed on the return, and the slide stop takes almost the full brunt of that force. He may be right -- or it may be that we need to just change them out, as we would springs, at some point.
You might ask this question of Angus Hobdell on the new CZ Forum; he is a wizard with all things CZ, a talented gunsmith, and shoots the gun for the CZ pistol team, too. He might know a solution. If I remember correctly, he routinely replaces the slide stops at a lower count. He may have better ideas. You can ask him ON/THRU that forum.
I wonder if a slightly heavier spring might work? The Browning Hi-Power variable rate spring from Wolff Springs comes in a 14 lb weight, and is a perfect fit for the CZ. (The Wolff springs for the CZ are really Tanfoglio/Witness springs, with a larger diameter that doesn't properly fit the CZ guide rod; the BHP springs do fit. I don't think the diameter issue has anything to do with function -- just looks.)
In the final analysis, as you seem to suggest, fixing your problem might be a case of fixing something that's not really "broke" in the first place, as that is a relatively high round count. The fact that the ejected cases aren't flying that far, and heavier springs don't send them far enough may simply mean you're stuck between a rock and hard place. Particularly if you're happy with your loads.