Lol Latency is dependant on your connection to the international server, (how quick it can get there). It does not matter how fast your line is as long as the information sent and recieved does not go over the amount of information your line can support. A 384 kb line can at least get 35 k/b's, While playing Starcraft 2 beta i have never seen my 384 line use more than 10 k/b's easily meaning the game is playable on 384.
Another point to make you stop worrying about latency is that starcraft 2 has a built in delay system making the game more fair for every user even if they are with higher ping. Everyone who plays the game has a set starting latency of 250ms afaik (it may be a different no. but same idea) So even if your right next to the blizz server your latency will be of 250ms meaning you just need to get less than 350 ms to play the game competively and you will only have like a 0.2 second disadvantage at the most.
I would suggest playing with a webafrica account for lowest possible latency and a 384 k/b line is fine for playing the game. So if you really want the game and are looking forward to it as much as millions of people including myself are. Get it and enjoy it without worry