i think the 3 MB test forward to 6 MB KB test if you score above 6 Mbps
but if you using SmarTest it dosent run all test sizes, it starts with a 97 KB testfile and depending what you score on that your forward to another testfile, eg if you score 5 Mbps, then your forward to 2992 KB test and if you score above 6 Mbps your forward to 6 MB test.
CABLE has more details about the rate of forwarding.
VanBuren
