I use the old DC not DCC. Sometime I run long trains that one engine will not pull. I will run more than one engine. I only match them up with engines with close to the same speed. There seems to be no ill efect. If you mean runing just the engine on the same tracks, that is something that I have a lot of fun with. It takes a lot of switching to keep them from crashing. I don't do this with good engines, just old toy ones.Is it possable to run to engines back to back?
Putting the faster engine in the lead is asking for trouble if the lead engine breaks away. I would rather "push" than "drag" the slower engine.I am in the process of DCC. I ran for years in DC and MUed all the time. Mainly for looks. I found that same manufacturer was no problem. Also different manufacturers would work some times. If the speed doesn't match put the faster one in the lead. You will probably find that different manufacturers will match at certain speeds as one will accelerate faster than the other and at some point the speeds will match up ok.
I too am in the process of converting my engines, switches, turntable.... Been a long process. I probably have double the amount you have to complete. I inherited may non DCC engines when my dad passed away in 1999. Still working on them. He was a big NS/NW fan. Lots of GP40's and such. I probably have 40 engines converted and another 20 or so that came DCC ready.I am not looking. I have the MRC Prodigy Advance and love it. When I said in the process I meant I am still buying decoders. I have 50 plus locomotives of which about 10 are DCC.