I have a dial up and can play online with few issues. Originally I just picked up free wifi signals and still played games online, then got my own service, hard lined from modem to ps3 and got around 6M/875k. Now I moved my tv and connect thru my wifi at around 70% signal strength and get 5M/875k. When I was "borrowing" my neighbors wifi I was getting as low as 15% signal strength from their wifi with 2M/600k and still got online & played modern warfare 3.
Only issue is you should not host a online race room, it can result in long load times. Lag happens from time to time but in-race lag is rare for me, people you race against will point out if they see your lagging.