With respect Bob, virtually all SDHC card maufacturers do advertise the
card's speed - on the card itself. You'll see a number (usually within a
circle) which indicates that card's speed and is called "Class".
Respectively,

Class 2 is rated at 2.0 MBytes per second.
Class 4 is rated at 4.0 or 4.8 MBytes per second.
Class 6 is rated at 6.0 MBytes per second.
Class 10 is rated at 10.0 MBytes per second.
Class 15 is rated at 15.0 MBytes per second.
Class 20 rated at 20.0 MBytes per second.
Class 22 is rated at 22.5 MBytes per second.
Class 30 is rated at 30.0 MBytes per second.
Class 40 is rated at 40.0 MBytes per second.
Class 45 is rated at 45.0 MBytes per second.

Regards...