I would start looking at Bryce's field test for the diffeent BBS coils, you can find them here
http://www.findmall.com/read.php?19,1055627. You also might want to read this post also, the 13 inch Ultimate coil vs the standard pro coil, you can find that here
http://www.findmall.com/read.php?19,1692757,1692757#msg-1692757. I have been on the fence about getting an 13 inch ultimant coil. The standard coil has found me a lot of coins, but if I buy another coil it will most likely be the Ultimant just because if can handle iron really good. Most of the sites I hunt has a lot of iron in them.
John
Minelab Explorer SE Pro, Quattro MP, Xterra 70, Sovereign XS
Whites Spetrum XLT
Tesoro Lobo Super Traq
Harrison City, PA