I went to Kicktraq and reached the conclusion that Fargo should call Chris Roberts for advice
That doesn't even count the RSI website, I think they've made over a million on the last day there.
They did more on the last day than in the first, which seems to way off the trend.
Project Eternity's 2nd day was 68,4% of the first, while Torment's 2nd was 34,7%.
The drop was bigger, but that's because the "response" to Torment was much faster. Eternity had unusually high 3rd and 4th days. Had it been pitched nowadays, its 2nd day would probably be a bit above the 3rd day it had, which was at 196k (~28% of the 1st day).
There is a trend in the last day for this kind of project which puts it usually at least 55% of the first day.
We're going to see an average of (at least)45k for each regular day from the 4th onwards, judging by previous projects.
Being (quite)pessimistic, we're looking at $4,096,464 minimum without paypal. I'd say $4.3 million+paypal, though.
Also, that's just me guessing, but there's a new factor this time around, Planescape: Torment fans backing a KS project for the first time.
I say it because the premise is very similar and the average pledge is $55, whereas Eternity's average was $54. People are paying roughly the same thing, but more of them seem to be doing so.
EDIT:
Numenara backers could also be interested in this, which is another potential factor.