Newman Atkinson says:

It doesn’t matter if you are running DC or DCC the engines should match speeds somewhat. Run selected engines near each other and find engines that hold about the same speed as the other through out the speed range It is really important in DCC or you will be spinning your wheels on one while waiting on the other to start rolling. Not really good on couplers either as they will be bucking each other I am running DCC and have teamed four engines together and all the engines have been adjusted through the speed range to closely match the others. This is especially important if you are using helpers mid train. You want them to pull evenly. In standard DC there is not much adjustment to even the speeds so getting engines paired as with MFG brands and size helps a lot. An example of bad matching power is the Bachmann Thomas engine The engine can be almost 1/3rd throttle before it begins moving and when it does it only goes fast. No way will it match the speed of my other engines. I have placed the engine on a zero-zero code on my DCC system which you can do on Digitrax but don’t let it sit there on the track and not be moving as it will heat up the motor in DCC. But in DCC I can make it creep and I can actually see Thomas Eyes move instead of a blur. So Thomas will get a DCC chip installed soon from Newman Atkinson