while I am not a big time beach hunter, when I made it to either a salt water or fresh water beach, I used the 950 coil. That was on the MXT, MXT Pro and the M6. The next trips I make to the beach I'll most likely use the 9" Spider coil because I like this coil, for a few reasons, and it has replaced the 950 in my personal arsenal. Both the 950 and 9" should provide almost identical performance.
I have hunted the Oregon coastal beach a fair amount prior to summer of last year using the M6 and I never had a problem. I also work some high iron mineralized fresh water beaches around Oregon and the M6 served me well. Matter of fact, I have worked a number of makes and model on both salt water beaches and fresh water, most with higher iron mineralization, and have thinned out all detectors from my personal arsenal except my favorites listed below .... all White's detectors.
Gone are my Omega and G2, Tesoro Bandido II