I think it's pretty cool that you like to tweak/upgrade the Bottlehead. I wouldn't mind doing that, but for me, I wouldn't stop tweaking and fiddling. It's better that I don't engross myself into yet another time and money sink hobby. I plan on getting another OTL some time soon. I've had several years with my Bottleheads now. I'm ready to move "up". I love the Crack w/Speedball for its price to performance ratio. Insanely good. The Mainline is spendy, but it is so much more refined, revealing, and pleasant to listen to. Where the Crack is pronounced, and likes to show off (Speedball), the Mainline kind of creeps up on you and doesn't have to show off. The Speedball is the hare, and the Mainline is the tortoise. It takes more time to get really familiar with the Mainline, but it just grows on you, whereas the Crack hits you right away, and demands your attention.