I started with the standard seat and a 250 mile day hurt!! I then sent it to Spencer and had the supracor update done. It was better, but still not great. I found damn near brand new Corbin on eBay for $300 shipped and bought it. It was better than the Spencer mod by a good margin. I was a happy camper until ...... I got the chance to buy a tall Corbin (I am 6ft 6 tall) and jumped at it. It's just perfect. I can sit in it (not ON it) for a whole day.
One thing you will hear people bitch about is how slick a Corbin is. A Corbin has a leather cover and as such unless you condition it, especially when new, it will be slick. Also I used to suffer from heat from the exhaust coming through the seat (I live in Texas) with both the original and the Spencer mod'd seats. The Corbin uses a much heavier/denser base and that issue appears to have been cured.
Here are some photos to let you see what the different seats look like. from left to right they are Spencer mod'd, Standard Corbin and Raised and lenghtened Corbin.