Its my understanding that Come On Pilgrim was literally the original $1000 demo recording -- e.g. allmusic.com says "Amazingly, Pixies' 1987 debut EP Come on Pilgrim was compiled from the quickly, inexpensively made demo tape — paid for by Black Francis' dad — the band made at Boston's legendary Fort Apache studio soon after they formed. 4AD was so taken with the tape that they released eight of the songs as this mini-album"
Of course "Come on Pilgrim" as released on vinyl would have sounded different from the cassette tape which got them signed but I'm pretty sure its the same recordings and would have sounded very similar. This re-issue is probably diffferent again but not substantially so I guess.
Anyway I would have signed them after the first 8 bars of Caribou. One of those "I can still rememeber where I was when I first heard it records".
Matthew
PS The b-sides compilation is worth getting if you don't already have it. See
http://www.pitchforkmedia.com/record-reviews/p/pixies/complete-bsides.shtml