The Z is fine at 250. I'd say its pretty decent up to 265 or so. Just don't stuff a bunch of crap in the stern and you're good to go. To this day, I think it's my favorite boat for really big water.
I always had a hard time fitting in the grind. It's a weird boat. Huge, but not a ton of space in the cockpit. I had a hard time getting it to fit...the seat was always too far back and I found myself staring up at the sky alot.