I have the Mustang seat and have had it for a little over a month, and probably 2,500 - 3,000 miles. So far I am NOT enthused with the seat and might switch back to the Stock seat. But, don't take that as a "Never go Mustang" comment, it could just very well be my butt that doesn't like Mustang.
I used to be able to easily ride 3-4 hours on the stock before even beginning to worry about my butt. Now with the Mustang my butt hurts after about 90 minutes. I jsut completed a 3-day ride in Colorado, so about 1,063 miles and my butt was screaming painfully by the time I got home. Not sure how it would have faired with the stock seat. From the Yahoo VN750 group, there are tons of VN750 riders who love the seat ... I'm just thinking I may not be one of them.
Two main difference with the seats are: 1) Corbin sits you lower, Mustang harder. Corbin is "supposed" to be a harder seat and Mustang softer, but mine feels like a brick. 2) Rear sissy portion of the Corbin is higher than the stock, while the Mustang matches the stock. This may not be an issue to you, butit was for me. I have installed the extended sissybar on my bike. The Mustang and Stock fit under this, but the corbin is too tall and would prohibit using the Extended sissy bar.