I've only run the 275/35-18 Rivals (all around, 8.5/9.5" stock width wheels) once this year, and that was at the BMW Performance Center CCA autocross. They did wonderfully, definitely an improvement over the 245s! Wear was excellent too up front. I got overall FTD at the event just beating out a nicely setup B-Street Prepared E36 M3 on BFG R1 (or R1S) tires too. They don't do PAX times else I'd have really cleaned up.
For an essentially totally stock car (just Dinan front bar), this thing is pretty amazing.
My local club has issues with venues this year, so we've only had one event, and I couldn't make it to that one; I should know more in a few weeks.
I do also have a set of 10x18 Apex ARC8 wheels with new NT-01s on them. I went the 2nd PC event with those a few weeks ago, and it was sublime. Unfortunately, it was extremely windy that day (40+ gusts), so there was no timing, but they were definitely going to be faster than the Rivals. I can't wait to try them out later this year. At least I offset the cost of these a good bit of this by selling a bunch of wheels I had for the M5 (full set of essentially new OEM rears, and 7 SSR GT-2H wheels, and five Hoosier A6s).
I don't think the E46 M3 will be as competitive as the E90/92 for the reasons you outlined, and it's front suspension is not as well designed. It can get about the same level of negative camber with the pins out (-1.4 degrees or so), but I think it's camber curve under compression is not as favorable perhaps? It's also hampered by stock width front wheels stuck at 8". I'll know more in a few weeks since there is an outstanding driver I know well in my local club who just bought one, has Rivals on it (245s all around I believe), so we'll be going head to head at events soon. Should be fun!