Hi, I am thinking of buying a 5" lcd screen, am just curious is this big enough? I know lots of people say bigger is better

, but seriously all i want to do is display cobra and maybe some video clips. I actually haven't seen a screen this size in person so am flying blind a bit. I drew up the dimensions and it seemed small just was curious on peoples opinions.
I notice most people have 6.4" or bigger is this due mainly to using gps?
Thanks