Yeah, unfortunately it's not really feasible to parallelise the loading process. If you'd been loading lots of separate files end-to-end it might have been doable with some trickery, but with just one file I'm afraid this is inherently going to be a computation which can only use half of a dual-CPU machine.

6 minutes is roughly consistent with the results I've been seeing on my 2GHz P4 (about 10 seconds per input megabyte). It is a pain, but I find lack of rewind to be an incomparably greater pain. (And anyone who doesn't knows where to find a lower-tech player :-)

Did you find any good Nethack recordings? The ones I'm coming across are already deep in the dungeon :-(

My current practice is to check alt.org's list of recent ascensions, pick one involving a character class I like (I'm currently playing Valks, so finding a competent Monk ascension is interesting but not immediately useful), and then look up the username on the ttyrecs page to find the ttyrecs corresponding to that ascension. There'll typically be a whole bunch of them as the game was saved and reloaded repeatedly during play. If you find the record which ends in ascension and it starts with "Restoring save file", then look at the immediately previous one and it'll generally be the previous instalment of the same game.

For example, on 29th November "firemonkey" ascended a Valkyrie. So we look up their ttyrecs, and we find that 2005-11-29.18:48:31.ttyrec is the end of that game - and the previous twelve files before that are also parts of the same game, so that the very start is 2005-10-26.16:41:42.ttyrec. (In fact there are a few thousand turns missing in the middle of this game, which is a bit annoying; I assume some sort of recording glitch, since one of the files cuts off without the usual "Really save?" / "Be seeing you" business.)