I had a 6'4 Proton (which was my step-up) which I loved in good waves (which was what I tried to only ride it in), but if I was eyeing a section that I wanted to hit down the line and there was any sort of flat section to get through, I kind of had to write it off what I was hoping to do.
I borrowed a 5'9 Spine-Tek OG Flyer for a few days, which was really close dimension-wise to the 5'11 Spine-Tek Fever I ended up buying (The OG Flyer was an 1/8" wider, but both are 27.9L) and much preferred the Fever. The Fever (IMO) just had more get up and go. I thought it still had some zip even in the thigh to waist zone, but my NB2 (Varial) has taken over low-end duties and is pretty hard to get off of on waves under head high.
The OG Flyer was perfectly fine, but seemed slower to react than the Fever. Hard to beat a Proton in good waves though. I've probably done the biggest hacks of my life on my old one and the biggest/best barrels. It sadly lost it's life on the monster swell that we had in the South Bay March of 2014.