Before making your choice, why not take the advise of those that say to contact Grady first. I've called them on several occasions, and they are very helpful, and will point you in the right direction.
Are the Etecs more expensive than Mercs and Yamies of the same hp? I thought the 4 stroke Yamaha would cost more than the Etec, but I'm not up on current outboard pricing. I do know my brother in law had a new Yamaha F250 installed on his '98 Seafarer, and it is fantastic. Easy starts, quiet, no smoke, super efficient, and powerful. Changed all my feelings towards 4 stroke outboard technology. Too bad they are so heavy.