how do you determine reel seat distance?

[labrax]

I am planning on building a spinning rod and a casting rod - both on older 11' Fenwick fiberglass blanks (SU1348). Was wondering if anyone had any recommendations on what the distance should be from the butt end to where the reel seat is located for each set-up. I guess it is somewhat personal preference - but is there some general starting point or guideline? I am 5'11" and have a normal wingspan.

Thanks for your help.

Pete