Considering most online games don't generally use more than around 128 - 256Kbps worth of bandwidth, you're never going to have a problem with bandwidth, unless you want to do lot of downloading whilst playing, in which case you're going to run into interpolation issues, buffers and other issues, which may be helped by having more bandwidth, maybe QoS in limited circumstances, but not much.
The biggest factor with cable is the line quality, if you have good CATV and well terminated cabling - it should be rock solid, however if you have problems with the cable itself, (bad signal, bad power, loss of sync, etc) it can be 100x harder to fix than DSL, as CATV (cable) is much, much more complex than regular telephone lines.
If you're on VM and it's good, it's probably going to remain good indefinitely.