Got mine mounted up last night and just got back from my HPDE at Pacific Raceways...
I'm running 275/40-18 on an 18x9 rim (the minimum recommended width).
In a nutshell, performance wise they are night and day from my "Ultra High Performance" all-seasons. This should, however, be no surprise..all-season tires do everything but don't really excell at anything. What was surprising considering the MUCH stiffer sidewall is that these tires came with only marginal increases in harshness and road noise. I would not hesitate to put this on a DD if you're ok with fast treadwear (for comparison, these have a UTQG of 200; my all seasons were 380, OEM GT500 tires are 220).
Track performance; these did well and impressed both myself and my instructor who has R888's on his M-Coupe. While I don't have a competitive racing background, he did so take that for what it's worth. They seemed to do rather well with high temps...I took them on a few very hard laps on session #2 and my brakes were fading before they got greasy (the caveat here is I'm not certain the pads were fully bedded at that time, they were fairly new EBC Yellows with 400 street miles and a couple bedding "exercises," and I may have been braking more than I needed to early on as I got accustomed to the amount of traction I had available).
They weren't perfect..#1 complaint is that I would have liked more feedback when at the limit. Steering feel could have been a touch better, but also keep in mind I am running these on the smallest recommended rim width (A 10" wheel would help a lot I imagine). Another thing to keep in mind is that these can be had for well under $200 a pop; I paid $650 shipped for my set on eBay, making them cheaper than my all-seasons. I don't think any other tire in this class can touch that aspect! Value wise, these make me wish I had more than two thumbs to give them assuming they wear fairly well..
Speaking of which, wear-wise...hard to say just yet. Here's a pic after the first 20-minute session; I'll measure the tread depth after I get some street miles on them to clean the tire goo off enough to get a decent reading. As you can see I needed to drop some pressure, I believe this was 36 psi hot..