Right now, I have a really slow connection, because I need to save some money since I moved apartment. I only have 8Mbit down (as opposed to 30Mbit before) and only 0.4Mbit up!!! (as opposed to 3Mbit up before!) - so I thought there's no way I can play wipEout online at the moment. But, it seems, these slow speeds are absolutely enough for comfort, as I've had absolutely smooth, lag-free races in the last couple of days. Only problem is that my wi-fi is very unstable sometimes (don't know why), so there are days when my PS3 won't even connect, I get a DNS error, or I get weird handling and heavy lag in races.
So it's definitely not about the connection speed (which means SL did indeed pull off a mighty good netcode), it's about the consistency of the data packets, and the ping, of course.