I am doing the same [1], SSH and tmux are my best friends. I did however try the expensive-powerful-laptop first [2], it wasn't worth it and my current desktop beats it in everything but gaming.
[1] $350 DIY PC + a $250 second hand thinkpad
[2] $2200 laptop with the latest i7 and discerete GPU.
I don't have an "ultra portable" but I have a $2500 desktop replacement for work. It's got a 970m and a 6700K. Yes, that's a desktop chip, and it hits 4.2GHz nicely when needed.
I mostly just tote it to the office and home, so it's quite nice.
I still drool over getting a sweet $2k+ ultraportable laptop though. I'll let my office buy those things for that work and stick to the cheaper personal life. Portable devices just can't seem to live with the chaos of life, and I'd rather break a $400-500 machine than a $2k machine.