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.