That would depend on what format card your Camera takes. I shall leave the technical aspect of this questions to those who know better like pixmedic and and our other long time members.
unless you are burst shooting and running up your buffer, its really not that big of a deal what card you use.
I got a bunch of sandisk pro class 10 cards (30mb/s) and a couple of the UC-1 sandisk cards (45 mb/s)
in 8-16 gig varieties. probably way overkill for the 2-3 consecutive shots I might take at any given time.
the regular class 10 cards are so cheap right now i don't see much point in going any slower than that, but unless you are burst shooting, i doubt you would see any difference between the class 4 and the class 10 cards unless maybe you were using a D800 in 14 bit RAW pushing out 50 meg files.
my D7100 does around 25 MB raw files and i cant shoot fast enough that my regular class 10 cards cant keep up.