Just to update the thread. I went for the 65, mostly because the power and transducer cables were the same as those fitted to the Garmin Striker already on the boat. As it turned out not only were the cables the same but even the old mounting holes in the console were the same. About as easy an upgrade as it is possible to get. As a bonus I can use the spare power lead to play with the chartplotter at home.
I finally got a the time to get out on the water today and everything works as I hoped. Size wise, only time will tell if I should have gone larger but for the moment for the cost in money and especially in time I'm very happy.
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