So I came here about an hour ago because I had the same issues on my 1st flight. Started cold and dark but skipped some of the startup tests (not sure this is the case) Threw 2 bags on and took off in Cat III. Roll behavior was slow as others have stated. Cat I or III made no difference.
I found this thread and tried again online. This time I did everything except MPO as it is in the EA guide. Clean jet with pylons in Cat I. Everything was perfectly fine and the Viper flew as you would expect. Cat III slowed the roll down slightly but still way faster than my 1st flight. Landed, picked up 2 bags, 2 120s on the tips and lost the pylons. The plane still behaved as one would expect.
At no time did I change any deadzone or curve settings on my stick from what I had initially set them to before the 1st flight. These are the same settings I use on the Hornet.
I will keep playing around to see if I can figure anything out and will report back