Although the catalogues don't say so, it's possible the differing varieties are from different mints, and the moneyers travelled to each one. I doubt that the trade of Moneyer was all that prolific! Value, again, depends on the collector. Those in catalogues are only guides. As in all auctions, two people bidding can lose the plot and bid way above published price. So you are looking for two collectors who specialises in Bristol coinage if you want the best price. A good specialist auction house will get you the best price. All that said, I don't think your coin is that special to get excited about! As I said, I'd expect £100+ at auction. Don't forget, all this is subjective and other collectors will maybe disagree!