Bill,
I have used the 4x6 and it does a good job, I seldom got any coins over 4-5 inches. I sold the small coil as I was not very impressed. Well a while later I wished I had a smaller coil for those high trash areas and decided to try the 5 inch excellerator coil, It is a super god little coil, I found several six inch wheat pennies in an iron infested area that drove the stock coil nuts. This little coil to me separates better than the 4x6 and I personally get more depth with it. I know ground matrix plays a role in depth but around here 7-8 inches is about the deepest coin I can hit with the stock coil and that was a quarter, then I got the 14 inch excellerator and it will sound off good on a dime at 9 inches, and the depth in sand on the beaches is almost to a point of crazy, in Atlantic city I pulled 5 quarters from 15-18 1/2 inches, now they won't blast your ear beeps but definately a repeatable beep. In my opinion the excelerators are the best coils out there for the mxt, I know others strongly argue this and stand firm with what they use, But to each his own and the excelerators work for me.
Ray