The ability to use 87-89 octane would definitely be a plus if you plan to drive your TA alot. Run a PPR TC-01 HF with stock e-heads and you'll be in the neighborhood of 500 hp, even with the lower octane and slightly lower compression. You would probably be able to run 87 octane in cooler weather, but put 89 in it during the the hotter months to protect your engine.
I built my 455 with a different purpose in mind- I was shooting for max hp w/ the SD e-heads, around 580-600 hp with their "Road Paver" HR cam. Dave Bisschop over at SD Performance recommended around a 10.25:1 SCR to run on 91- great for hp, but not so economical due to the price of 91. My 72 Esprit will become my demonstrator car for my business, so it's not going to get driven alot after it gets rebuilt.