I was looking at those two also. This is about all I came up with, cut and pasted from there website: The Gold Bug will now be available for $549 without the manual ground balance, no VCO in discrimination and slightly less sensitivity to small nuggets than the PRO model.
The Super hot Gold Bug Pro is redefining gold prospecting and the relic hunters love it too. Many of the features pioneered on this unit and other FTP products are now being emulated by other manufacturers.
If you prefer the unit with the 11” coil as standard go with the Gold Bug DP $749. ............ This is a page that might take you a little farther:
http://www.fisherlab.com/hobby/news.htm .......Of course these prices are MSRP, expect to go about 50 bucks less than this plus package bonuses One dealer is offering Grey Ghosts and Lesche with the Gold Bug DP for $700. Since I was just going to spend the money on a pair anyway, that brings the price down $100 bucks for me. The gold Bug DP is just the Gold Bug Pro with the 11" DD coil. All the Gold Bugs are the same 19 khz operating frequency. They also have now come out with a 5x10" solid DD coil that fits all GB's and the F5.