Originally Posted by enigma
The wider tires are probably worth 0.3 to 0.5 all else being equal.
You should try running both tires on the same car at the same event. Last time I did this the difference was a lot less than 4s. I have not tried A6s on the E92 M3 yet. I have tried race & street tires on the old E46 where the V700 (older Kuhmo) was about 1.9s faster than my street tires. On the elise I have measured the hoosiers as about 0.5s faster than the 048s (M). Now this is on one lot (fine grain concrete), test at a different lot and results will vary.
 The last GRM tire test had:
1. 42.984 Falken Azenis RT-615
2. 43.254 Falken Azenis RT-215
3. 43.287 Yokohama Advan Neova
4. 43.511 Hankook R-S2 Z212
5. 43.762 Kumho Ecsta MX
6. 43.855 BFGoodrich g-force T/A KD
1. 41.008 Kumho Ecsta V710
2. 41.142 Hoosier A3S05
3. 41.217 Hankook Z214 C70
4. 42.428 Yokohama A032R S
The A6 is slightly faster than the A5, espically on camber challenged cars.
This is good information, as the Grassroot MotorSports guys perform these kind of tests once in a while.
I have been running Hoosiers since the A3S03 up to the R6/A6. I also ran V700, V710, RA1, Dunlop/GY/Michelin/Yoko slicks, MPSC, MPS2.
Although all my tire tests have been done in different cars (Boxster S and 911 GT3), I use either the same track or the same autocross event to compare them.
The V710 was a quantum leap forward for high horsepower cars. I was running 273/35 and 335/30 A3S04 and A3S05, and I could not get that much better grip than the A3S03 at my local events. When I switched to 245/285 V710, I gained 0.7 secs over my wider A3S05 on the same course. I ran these narrower V710 and got very good results locally. Hoosiers were suffering from early cords back in the day, so I quit Hoosiers.
When the A6 showed up, I was expecting same problems as the A3S04 and A3S05 (the A3S03 was great). All of a sudden, guys running A6 were improving their times, so I gave the A6 a try.
I ran the V710 and the A6 at the same event, and I gained close to one second on a 45 secs average course. This was with 285/335 A6 vs. 285/315 V710 (the V710 sizes I ran later). My V710 were fresh when I tested this (-30 runs).
After that I just ran half the events on shaved Toyo RA-1 and the other half on A6, or a full event on RA-1, until recently. A6 brought my car close to a National Championship in a class where people run slicks (FP), my co-driver won a National Championship with this same car.
The street tires tested by GRM are the choices for the Street tire classes, plus another 3 or 4 new tires, but the PS2 was never an option to win the ST classes as it was not competitive. Let's assume that the PS2 is as fast as the BFG-GForce and Kumho MX (and it isn't), we are looking at a 3.8 secs difference between PS2/GForce/MX against V710, before even considering that the A6 is faster than the V710, or considering wider A6 tires, and we are already assuming that the PS2 can keep up with these two street tires.
My experience with the Lotus Elise has been short (students or friends drives), but the A048 are not even close to MPSC performance, let alone V710 and A6. You should see more than 0.5 secs difference between A048 and A6 with the Lotus, this is assuming you're driving at 10th/10th (limits of grip on the intended line).