Al- Yes, the 1st in the 912 is noticeably taller. I can easily bumper-hug Miatas through the widest four lane intersections in 1st without resorting to screaming rpm's. Most of my experience in the 912 is comfortably torquey in 3rd and 4th which nicely handles everything I've encountered...in fact I can count on my fingers the number of times I've loafed along in 5th. (Downshifting into 4th to pass tractor trailers is an adrenalin kick in the butt!)
Now, the 912/911 people numerically identify their gearing alphabetically!...I haven't found information that converts A, B, X, etc. into numeric ratios., but I suspect that stock 901 gearing in the 912 would compare favorably to 'ideal' conversion combination$$ this thread is promoting.
For that reason I've got a 901 (pulled from a 912) collecting dust, alongside a complete IRS to bolt it up to, patiently waiting for me to acquire the knowledge, balls, and confidence to tackle such a conversion!!!...Audacious considering that when I purchased the VS my entire 'tool kit' consisted of a few wrenches, a couple of screw drivers and a cartoonish 437 page John Muir manual "step by step procedures for the complete idiot"...Ironically very appropriate.