Yes the gearing is about the same in the M3 and the stock ZHP. Throw a 3.62 LSD in there you'll be at 56mph in 2nd gear and not even 85 in 3rd...you should be able to hit 102 in 3rd gear with the 3.07 and a 7000rpm red line...which is pretty incredible on the track.
Michele, your car is S/C'd so I wouldn't worry about doing the M3 rear end swap, just build the 3.07 or get a 3.38 or 3.46 built into an LSD.
Assuming you have a 7000rpm red line with the S/C software and 255/35ZR18s out back:
With the 3.07 LSD, speed in 3rd is theoretically 102.27 mph - Cruising at 74mph (9mph over 65 mph speed limits) is at 2593 rpm.
With the 3.38 LSD, speed in 3rd is theoretically 92.89 mph - Cruising at 74mph (9mph over 65 mph speed limits) is at 2855 rpm.
With the 3.46 LSD, speed in 3rd is theoretically 90.74 mph - Cruising at 74mph (9mph over 65 mph speed limits) is at 2923 rpm.
With the 3.62 LSD, speed in 3rd is theoretically 86.73 mph - Cruising at 74mph (9mph over 65 mph speed limits) is at 3058 rpm.
Sorry...I am quite bored with this English paper LOL...Hope these calculations can be of help.
http://www.bokchoys.com/differential...calculator.htm