There might be a negligible decrease in speed since 220 bytes less are being transmitted per frame, but I don't think it's a breaking issue. Problems arise when the MTU is set higher than all parts of the network can handle, which is why the standard seems to be 1500 (although I've seen some openvpn configuration files restricting the MTU to 1400 for reducing packet loss -- I've never tested to see if it works or not). I'm not sure why your NIC is broadcasting an MTU of 0. Someone more experienced with the (Arch) Linux network stack should be able to help here.
