I doubt the speed of the network link is going to make a difference on DOS games, whether TCP, UDP, or high speed networks are used.
From the perspective of a programmer, the network was another slow device to deal with. If the network started magically responding 100x faster it probably wouldn't affect the game in a negative way, as network communication is inherently asynchronous. (You fire a packet out as you need to, or you get the interrupt when one becomes available. You don't sit and do anything timing sensitive that depends on packet arriving because you have no idea of when that will happen. Packets drop. Timing is affecting by other things on the network.)
Also remember that back in the days of 10Mb/s Etherne people were using hubs, which were subject to collisions. That problem basically doesn't exist anymore since everything is connected to a switch now.