Their TVD model is clocked faster since it has faster memory (3.3 ns I presume). It is like the Albatron Geforce4 ti 4200 Turbo with 3.3 ns BGA DDRAM. Usually, the Geforce4 ti 4200 is clocked at 444mhz (memory), some of the more recent ones (i.e TVD and Albatron) are clocked faster, but are also a bit more expensive. So, to answer your question, no they are not overclocked, they are simply equiped with faster memory allowing higher clock speeds.
"Hey!! Who's that hiding behind the bush??!...Well Wingding of course!"