410 is it for me, too. I didn't know a regular commercial jet ever went higher than that.
The most surprising plane to cruise at that altitude that I was on was a DL
CRJ, believe it or not! It was from Wichita to Cincinnati, and we went up to 410 to go over a storm.
My first time at 410 was on a DL
767-200 - The Spirit of Delta, in fact - on a flight from SEA
Those who want to do something will find a way; those who don't will find an excuse.