I never heard that card slot speed is limited. Usually it’s depending on the SD or SDHC card.
Where did you saw a SDHC card with 60 MB/s? Fastest SDHC card is known to me is SanDisk Extreme 30MB/s and they are really fast. I only use this brand of SDHC cards and never had any problems with performance or something else. They are fast enough for recording FullHD movies for example