I do like e-85 very much the more I use it. This fuel requires about 27-32% more fuel for the same amount of air. From volume to main jets. This is a big reason my car is taking EVEN LONGER to get out to the races.... Been giving me a lot of headaches along the way. That said, the fuel is very forgiving and appears to let you go "lean" without melting plugs/parts.
The modifications to my webers is immense compared to a stock 48. Lot of trouble not only getting the fuel TO the carb but getting it from the bowl to the jet to the venturi.
My engine is probably at the limit of using a 48(mine are 52) as far as hp is concernd with the bowl capicity being the main restriction. I recently upgraded to a full Magnafuel system with all new line and regulators and I was still having trouble getting fuel to the bowl (needle and seat being the restriction). I am working on a new N/S idea to save a lot of headaches for future vw weber racers at the moment.
The practical limit of pump gas E-85 is pretty high I imagine. I am blending my own 85 from 98 with a special fuel so my limit or octane rating will be much higher. I have read that pump 85 octane rating is around 107 but it cant really be compared to a race 107 as the fuel is different and ethanol has THE highest anti-knock of any fuel available.
E-100 has a rating of just over 129. The pump version is so low as they use the cheapest gas possible to mix with it to keep costs down. 70octane is the number I have heard as a de-naturant. This is the reason for the low 107 rating.
I havent dyno'd my car but I will say this, so far the best mph has been 124.4 running lean still. At that run the air was 2600ft and my car weighs about 1620 ready to go. Corrected hp would be around 265-270 on that pass if my calc is correct.
I am not concerned at all with the fuel I am mixing having a hp limit as I have talked to a few big time nitrous guys pushing it a lot harder than I am and have zero issues.