Hey Phil,
On my 800L I did 14" butt grip and 5" fore grip. It's probably an inch longer than I should have but not terrible. On my Rainshadow SW976 which is more like the 800XL I did 12" butt grip and 5.5" foregrip. That feels just about right to me. I would measure from the very tip of your elbow to where your hand would grip the reel naturally. Hold another rod to get it right. You want a fair amount of leverage in the butt section. A short butt section will tire you out when retrieving the plug all day.
I have fuji trigger reel seats, don't know the model. Brian probably does. Samurai TI on the bassntubes board has an 800XL so you might ask him what components he used.

-Rob