While discussing the development of a network component for our game engine, a member of our team suggested that transmitting either 500 bytes or 1k of data using UDP makes no difference from performance perspective of the system (the time it takes to transmit the data).

He actually said that as long as you don't cross the MTU size, the size of the transmitted data doesn't really matter as it's all the same.

Is that true for UDP? what about TCP?

That sounds just plain wrong to me, but i am not a network expert.

*I've been reading about other companies' game networking architectures, and it seems they're all trying to keep transmitted data to a minimum, making my colleague's claims seem even more unreasonable.