I had 4.10's in my previous stang... I now have 3.73's in this stang, and I can say that I like the 3.73's. They are a great gear for around town and on the highway.
Not sure if the speed cal's will work on our cars or not... My speedo is already corrected. How it was done, I do not know. I haven't looked into it.
As far as the 4.10's go, the chip prevents you from hitting the rev limiter, or so I hear. I'm gonna go with everyone else. Save the money for a converter.
Just wanted to point a few things out. 3.55's are the highest gear ratio you can run with only a speedo gear change (and still be accurate). I use a Dallas Mustang SpeedCal in my 1995 5-speed with no problems. It is accurate within .1 mph. The install only took an hour or so, and to me was well worth the money (my car came with 2.73's and the change to 3.73's had me getting passed on the highway while my speedo read 115 mph ).
Thanks man, I was damn happy with it considering I was running with the 01-03 Gt's that were out there and even beat a couple. I'm hoping for some better times in a couple of weeks.