i went opti as well and it was a choice between price, power, weight, looks, warranty, resale, other unproven units at the time.
i went opti and very very pleased with it, lots of oompf and good economy and a great noise.
if you think you are going to be as quiet at lower speeds as a 4 stroke then forget it but at cruising speeds and higher speeds it is absolutely fine. Some people complain they are noisey but perhaps they did not get out there and test ride some and do their homework properly.
try to test ride a boat with one on the back and if you like the noise then you are all set.