I have not encountered a fixed jet carburetor in any 10-10 models that I can recall. I have them in a CP55, PM55, 7-10, SP105, and SP125 that I can think of off the top of my head. None of them will rev wildly out of the cut, but they all work hard in the cut. The 105 and 125 in particular need to have a long bar and a pretty decent load in order to clean up.
I have an LG6 that came with a governed Tillotson but I could never get it to run properly so I replaced it with a fully adjustable SDC but to be honest, my worn out 2-10 G still seemed to be faster in logs up to 20" or so. It's not always just displacement that matters, torque and chain speed are important factors as well.
If you are cutting smaller stuff (under 4") then it's likely a modern, high revving small displacement saw will be faster unless you get downright dangerous on the depth gauges on the 10-10. Alternative would be to try an 8 tooth sprocket and see if that helps on chain speed. Or just wait until you get into some larger diameter wood and then show your buddy the advantages of having a little torque to spare.
The Echo is likely running 3/8 LP or .325 chain which has a smaller kerf and is therefore removing less wood which helps keep the chain speed up as well. I'd say use your 10-10 as intended and don't worry about a few cuts in smaller stuff.
Mark
P.S. Make sure your chain is sharp and the depth gauges set correctly...