As far as I know the current PC build has some processing leak that crushes all speed runs anyway. (Unless that got fixed already, but I don't think it was clear why it was happening. It's a bit mean to ask it to just slap out 16x flawlessly on any old toaster... but some of the builds have anyway it seems.) The only reason I can try anything right now is I've got a Mac - and some really weird issues getting updates. On the flip side I can't get the secret books, which for a NG+ run means I can't seem to do much better than my 6 hour 50 minute run. (This should remain a category, but 'tis pretty hard core. Any time you need to pre-stock a Nalgene for liquids before you start... ya.)
Even if you can roll back to the previous build somehow, you're going to have to keep the graphics down to around original settings. I was marveling at how solid speed was on the HD re-release. A friend of mine tried the demo, and first thing he did was set it to full 1080 HD (or beyond?) - and it didn't even play the first levels at 1x speed. (Also Mac, so we get some weird extra problems sometimes.)
I can attest though that the legacy build (which I still have, cause again, weird deploy problems for me at one point), even capped at 4x speed instead of 16x, can be pushed to the 1.5 hour range. Not competitive any more, but a good way to get some practice and routing while we wait for the next build to fix the speed problem while still having all books.
That is one very nice thing to consoles though - until recently, it was basically the exact same hardware for everyone, so getting an advantage with a "better rig" didn't even make sense. When operating as intended though, the PC build is close to that. And if enough people get into it, Lars sounded open to trying to tweak out an option to support it, so that maybe the game itself can report times without loading counted or something like that. (Although it probably needs a maximum load time grace amount, or you'll be trying to run on slower computers to catch a longer breather!)