Have you tried Gummi? It's an editor with auto-updating PDF preview. It doesn't improve on compile time because it just runs pdflatex behind the scenes, but I find it usable when designing figures using tikz.
I use texpad which has auto-updating PDF preview, it does partial builds so often even with a large complex document it only takes about a second to update (although this is too long in my opinion). Occasionally it can't do partial builds (some libraries screw it up) and then I'm stuck waiting 10 seconds or more for the preview to update.
