Hi Giltron,
No particular reason for purchasing 8" coil other than to try one -- after using it I find the 11" coil a bit weildy and heavy. Sunray was chosen because they work in conjunction with Minelab,-- and not to say other coils are inferior. Really happy with Sunray, have one on the sovereign as well ( 8" )
For beach hunting I put the 11" coil back on and have a 12" Sunray for the Sov --covers more area but only a little deeper than the 8". -- probably an overkill as the standard 10" sov coil is very good.
Baz