Re: Mark VI?
THe Mark VI is a great horn, but since you are familiar with the Yamaha YAS-23, I would suggest a YAS-62 series II or YAS-82Z. Yamaha makes a fantastic sax, and for the price, they are pretty hard to beat!
If a vintage sax seems more appealing, try a Conn 6M, Buescher 400, or King Super 20. All generally sell for less than a vintage Mark VI, and are arguably as good or better than a Mark VI!