I have the 8' 6" 6wt and yes, the butt section is bigger. I busted a reel seat trying to ream it to the right size. I ended up cutting off the bottom and fitting the reelseat on with a stent. It also is lighter than the other modern glass rod's I've cat. I own a lot of 6wt's and this is my favorite modern glass 6wt. I still fish vintage 6wt's for fun (Fenwick, Phillipson, Silaflex, as well as early Fenwick and Orvis Graphite) but the GTX is my top choice in glass. In graphite, it is the Rainshadow Eternity^2 and McFarland Tailwind, for the times I need high line speed or a 9ft rod.

Ive cast a few GTX 7wt rods. It is on my list of rods to build out for smallmouth. Occasionally I feel undergunned with the 6wt with 50 ft casts with bigger poppers. The GTX 7wt is also big in the butt. It isn't quite as light as the 6wt, but for a long glass 7wt, it's still light. It is a much better choice than the GTX 866. It has much more lifting power. He also makes an 8wt that I've considered for this purpose.