Over water can have additional issues with reflection(s) causing signal variation, i would check that this will not be an issue before purchasing expensive links?
Depends which frequencies you can use from this licensed band. My experience is not very good unfortunately, it may have the same issue as SXT6 (http://forum.mikrotik.com/t/6ghz-products-not-working-well-at-6300-mhz/114897/1) where signal levels drop sharply at >=6300 MHz (yes I have contacted support, not much help), and at lower frequencies (<6100) NetMetal5 in superchannel mode with good 6GHz panel antenna (ElboxRF 23dBi) had a few dB more signal too.