I don't really pay attention to whether or not a table is fast. I just select them based on stats.
I remember other multi-tablers (specifically Zachvac) have said they don't pay attention to table speed when selecting tables as well.
There might be a slight difference, but when you enter the game you become 11% or 16.6% (for 6-max) of the table stats which I'd guess compensates for that slight difference.
I'd be interested to know if there is a significant difference. I mean, they're bound to attract some people who seek them out, and people who just pop in randomly might make hastier plays?