I have some feedback to share on the RE71Rs after the SD tour. This is on a CS car.
1.) Qualcomm Stadium Surface is very slippery and rough. I hadn't run here before, and I was surprised on my first few runs on how slippery it was. I think the RE71Rs were a better tire to have on this surface, but I think the loose surface helped neutralize some of the inherent advantage the RE71Rs have over 'lesser' tires. In other words, they would still have more grip relative to another tire but not to the same degree like it would on a good surface.
2.) The TnT was held on a different lot, the surface was better there. I was impressed by their level of grip and thought they held on better than my RS3s did. It was just a TnT, but raw times were better or very competitive with STR and STX cars on Z2*/RS3s.
3.) I would like to see how they do on a surface I have more experience with and have driven my RS3s on for a better comparison, but based on my experience from the TnT site, I expect the RE71Rs to be faster.
4.) Turn in is good, way better than 245/40 RS3s that are pinched on a 7" wide wheel. I hated the floppy RS3 sidewall.
5.) The wear on these are horrible. Easily my biggest disappointment with these tires. My co-driver and I put on 24 runs this weekend, 12 on the TnT (30~ seconds long), 12 during the NT (50~ seconds long), and the wear is incredibly poor. I think some of it has to be attributed to a fast course with a rocky surface cutting into the rubber, but looking at other cars in grid with Z2* and RS3s, they didn't look nearly as bad. Pictures of my front driver's side are below. Yes, that from just 24 runs, maybe 30 street miles. I took the photo with the tire in the wrong orientation. The right is the outside, left is the inside. The rears had the same surface texture, but wasn't as cut up. I will need to rotate them for the next event.
So with all of this said, I'm a bit conflicted. We are still waiting for the Rival S and V720s, but from the tires we have today, the RE71s look to be the fastest 200+ TW tire. You'll want them if you want to compete, but because they wear out so quickly, I don't think they are right for everyone.
If you want to be on the very edge and forefront of competitiveness, these are the tires you'll need. But be warned that if you attend multiple events per month, you may have to buy another set before the season is over. If you have a co-driver, then you may be looking at multiple sets a year. This part frustrates me the most since the whole point in moving to street tires was to have cheap but competitive options. I don't know how long these will last, but the wear on my set was significant after just 24 runs. Hopefully they'll wear better on a different surface and as the tread blocks wear down, but 'Street tires' only capable of 100 runs is no better than where we were with Hoosiers.
For reference, my first set of RS3s V2s were grippy until about 150 runs, then they heat cycled out. But they still had tread for another 150 runs. We tossed them once we hit about 320 runs and about 2k street miles.
If you are just starting autocross or just doing it for fun, I have a hard time recommending these. I think you're going to be better off with a Z2 or RS3. They are still plenty fast, you'll still be competitive, and they'll last you twice as long.
For me, who already has these tires, I'll use the RE71Rs for 'special' events and won't burn them up on local events. They wear far too quickly for that. I am fortunate that I have two sets of competition wheels, one with RS3 and another with the RE71Rs. The RS3s are going to be our 'practice tire' and we'll use those for locals until they're dead. We might try a Z2SS in 235/40 next time around. Once the RE71s wear out, we'll know more about the Rival S and V720 and I may try them out if they are competitive and wear better.