I think playable is meant more in a "we can have a fun game" sense and less of a "I can be competitive at a high level" sense. Even the former becomes hard at higher latencies.

Sure, I'm using 4 G mobile internets now and occasionally have to play call of duty at around 80 ms and I can still kick ass. There's no place like LAN for hardcore competitive gaming but if the game's netcode is done well 80 ms is good enough. The trick is to have some sort of lag compensation, which cs should have as far as I know, where you don't have to lead your shots so the feel of the game is mostly the same, you just get the reports a bit later than you would at 20 ms.