Yea, conversion does take a lot of time and that is the biggest problem. The issue is that i'm not writing the tools myself and can't really do any optimization. Ghostscript is surprisingly slow at rasterizing and autocropping (Adobe Reader can display a page in under a second... ghostscript will in some cases rasterize it for MINUTES), and then the image tools are also fairly slow at doing their steps. Maybe I should try to recompile ghostscript and imagemagick to use SSE (i might be using 386 binaries.. ill check).
The two big settings in pdfrasterfarian which affect speed are:
autocropping (adds like 10 mins per 100 pages)
boldness value (the lower the faster. much faster)
In the end, though, you'll be spending a week reading that 300 page document, so an hour to convert doesn't seem too much of a deal-breaker. But I'll see what I can do compiler-side.