It'll depend on how much time you're on the throttle (more open tracks will use more gas), but I typically drain a full tank of 94 in a lapping day. That would be six or seven 15 minute sessions. With e85 running richer already, plus making more power, I would guesstimate you're going to need 30% more fuel per day on a similar track.
Assuming I would burn about 12 gallons of 94 on a tighter track, adding 30% is ~15.5 gallons per day. Even if I'm not super close, you're still well under 55 gallons in a weekend. Your mileage would have to be a 100% increase over mine to burn up close 55 gallons in a weekend.
I've emptied my tank many times here:
I haven't run any full days on the CTMP GP track, but I've gone through about half a tank in two 20 minute sessions:
