I use a Hotshot coil on my DFX alot but that one was specially designed for the dual freq and also the MXT as well,i rate them alot and not only are they deeper than the stock coil and by a fair old margin as well they are so ultra light for the size,one of my favourite coil.Its not only deep on of course larger target but it still retains the sensitivity to smaller items as well.
Anything bigger than 12'' and you start to loose that sensitivity,not only do i use one alot but also have a backup one as well,as the guy who built them for Jimmy Sierra pass away a few years back,so they are a pretty scares coil to find these days.
I still cannot get over the fact of how light they are,they must be i guess foam filled or something like that rather than say resin which would weigh alot more,i rate them very highly on my DFX,the folks who use them on the XLT also rate them alot as well.