Thanks, that's me...I'm a excal lover...
On the shaft I think I've tried them all, long ( Florida long shaft..Balanced out, very easy to swing, good for big coils, excal stays out of the water up to about chest deep, making it a little easier to swing, less resistance) ..............med length (which is just about the same, but had problems with it hitting my back), and the under the elbow. For me I like the under the elbow, seems like I have better control of the coil, it almost feels like a extension of the arm once you have it strapped in. I just finished 2 carbon fiber shafts, one has a WOT coil on it (14 inch coil) and the other will be for the 10 and 8 inch coils. I added alittle more length to the larger coil shaft to help balance that weight out...so it sets back about 6 inch's more then under the elbow shaft. One thing I did do on both shaft was change out the lower shaft for a White's tallman lower shaft..gives me a choice (by adjustment) of a wider swing covering a wider area. It is about 10 inch's longer then the stock Minelab lower shaft.....
My opinion, if your going for the waist deep to the dry sand..10inch coil...And it sounds like your in good shape..go for the overunder, I've seen several of there shafts and they are very nice. Good Luck, let us know how this works out.
Be good to hear from some of the Florida users on the long shafts...