Twin 140's will give you more speed than you can use most of the time while offshore. The issue of planing at slower speeds is a real issue, and I heartily recommend trim tabs. With tabs you can run the heavy twins on plane down to around 15-16 mph. However, with 140's, you will have difficulty planing with only one motor unless you have pretty big tabs.
Considering the price difference for Merc Opti and Verado, and Yamahas, Zuke is the way to go. Currently $15K for CR 140hp twins from Eds Marine Superstore, compared to $19.5K for CR 150 Yamahas, and 18.5K for CR Merc Opti 150s, and $23K for CR 150 Verados.
Of course, you could always go with left-over '07 twin Tohatsu 140 2-stroke commercial motors for about $12 K.
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Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury