I'm 6'3" also and have the Ultimate King with driver backrest which replaced the stock seat with a Show Chrome Smart Backrest. I need lower back support more than anything and like the Ultimate backrest better.

I think the Ultimate does drop you down a little but I couldn't tell. It did move me back which I like.

I thought the stock was okay and better than most stock seats, but the Ultimate is better. My eyes give out before anything else on me does and I've done a 1500 Iron Butt.