I rode last week on a hardpack track both a '13 350 and a 450. Weighing in at 220lbs, and being 6 ft. i'm not a featherweight. The 350 was totally stock, the 450 was fully adjusted for a national racer, incl. heavier springs front and rear. My present bike is a '05 RMZ 450, but I'm dealing with the same problem as you do. The 350 should be the perfect bike for your weight/length, as far as you can manage a fluent riding style. You have to keep the speeds in corners more constant, while the 450 accomodates a more edgy/square riding style. The 350 feels like a very well steering /beefed up 250, while the 450 gives the 'wow what a powerful bike' feeling.
This weekend i will try the 350 again on a sandy track, so i will post again after the weekend.