I want to see a tire test comparison! I firmly believe the rally tires you are currently running are WAY too HUGE. I bet you'd see a significant reduction in times by going with the smallest 15" tire you could (yoko sells 185/60R15's, which are slightly smaller than the factory 16's with 205/50R16's on my 1995 STi).
Considering the data you collected from running the auto-x Miata, I think it would be very worthwhile (and the n/a 2,2L needs all the gearing help it can get)!
The only reason I could see to stick with the taller tire would be a faster course... but even then, I always find that (for instance) in my 2.5RS when I had taller winter tires, the extra entry speed made it very difficult to properly setup for corners (the 5km/h is make or break in the tricky stuff, especially in such loose conditions with tight corners). Combined with the hopefully "quicker" acceleration to the top speed bouncing off the rev limiter, I think the time spent travelling down the short, typical rallyx straight would be negated.

