evolutionmovement, here is a thread on taller final drive experimentation
MX-5 Miata Forum - 6 Speed, 3.636 Geared, NA Miata
BTW I don't think the RX-7 trans just bolts in. IIRC, swapping in an RX-7 rotary and trans is more difficult than swapping a V8, much less using the trans with the original engine.
And here is what I mean by staying in each gear longer to compensate for taller final.. Let's say at 30mph you'd normally shift to 3rd gear. Well now your rpms will be a little to low, so instead you stay in 2nd gear until 35mph. No performance loss, you might even gain in some situations because that 30-35mph is done at higher rpm