Hi Mike,
If all fuels, including 98 and 99 octane spec contain ethanol within the U.K, then richer needles would definitely be required as the blended fuels don't deliver as much energy per unit volume. Fuel consumption increases and performance is reduced. To me, even with a blended fuel, both the BCA and the BAC have the wrong profile for an otherwise standard road going engine, even taking into consideration the variations that you listed.
I know Tor tried needles suggested by the Winsu program and his engine ran terribly rich. I suggested a test he could try and an alternative needle. The test showed his engine was running too rich, so he changed the needles and performance was restored. LeeEFI also had a similar experience and gave a warning of what can happen when the needles are wrong for the application.
There is however a fly in the ointment, Stan (vaultsman) runs BAF needles in OCCY, K & N filters on the end of the elbows, SD1 heads, 3.9 camshaft, and he says that it runs beautifully. He tried a richer needle to start with, but found the BAF was much better.
Something to consider, would a 4.6 litre engine that draws 30% more air compared to the 3.5, require a richer needle than the BCA or BAC?
Ron.