When I said 10,000 towable weight, I meant including the trailer. I just looked at the weight of the 283 on the Grady site and it stated just under 5900 lbs. Add fuel, engines, gear, anchors, etc. it'll go up fast, but your 12K lift should be fine.
A BIG difference in ride? Probably. Someone with real experience aboard a 283 should jump in here 'cause I can't say for sure, but logic dictates a big improvement. I went from a Seafarer to a Gulfstream and noticed a noticeable improvement in ride, and that was going up just 1 ft. I have to say the 9' 3" beam of the Gulfstream helped, as it will for you when you go up to the 283 from the Journey.