I was able to use my home computer lag-free at my highschool when it was at home sitting behind a shitty ADSL connection. Later I used it at college with my computer at the dorm with a 100k/sec upload cap (enforced to discourage student file sharing). It pulled some dirty tricks with X forwarding, caching pixmaps, and jpegging the hell out of the individual elements, but it really felt like the computer I was using was right there.
What I don't like is that Parsec relies on third-party servers for the session initiation, and that streaming Linux desktops is currently not supported. Maybe the open source implementations of Nvidia's GameStream (Moonlight and Sunshine) could be an alternative.
Its better than the Windows client because it just works as another desktop in the Mac OS, with no bar at the top, and you can jump in to and out of various remote session quickly just by switching desktops with Cmd+left or right arrows. Its a really simple, nice to use implementation.
For low bandwidth/high latency links, RDP easily wins.