Opinions welcome, with a crew weight between 250 lbs when solo "most of the time" and 450 lbs with crew. will the 18 be way over loaded with that much weight (450). will 250 be enough to keep the 20 down in anything above 15 kts of wind. I'm familiar with the I20. Opinions and comments on the 18 would appreciated, also comments on the NACRA f-18 vs the I18

450lbs on the I18 certainly would not be competitive, but yes you could sail on it no problem. I18 has less freeboard than the F18 and I20 so if you have a lot of chop then it might be a problem. You could single hand the I20 up to 15 knots. I wouldn't use the spin or the jib and you would be in survival mode above 12. If you are single handing most of the time then an F18/I18 or F17 would be a better match. I would even go for the F17 with the bigger spinnaker if you want to race.

Never promote anyone to sail a 2 handed boat on their own.
Sailing them is easy, getting up from a capsize or out of trouble is another story!
There is no cat that will single hand and than carry up to 450lb and be safe all the time. No matter what they will tell you at the boat shows.