To get an idea of how the Kindle's PDF to MOBI conversion will do, try importing a PDF into
Windows MobiPocket Reader. It will convert to MOBI and display the results. If they look good, then Amazon's conversion will likely work (or just side-load the WMR MOBI version, which will be in My Documents\My eBooks).
To get an idea how PDF reflow will work on practically any reading device except the Kindle, try reading it in
Sony Reader Library for PC or Mac. In SRL, Small is the original full page and all other sizes are reflows (e.g. Medium) if a reflow of that page is possible. Note that the screenshots are of a 600x800 reading pane (as on most E-Ink readers), but this will likely be much larger on your PC's screen than on the reader itself.