Echo has a few "home-runs" in their line-up, a few that are just "OK" and a few "turds" as well. I've not ran some of the newer models on your list, like the 4510, 4910 and 7310 so can't comment there.
Pound for pound a CS-510 is difficult to beat in the 49-50cc range and don't be fooled by it being a "clamshell" design, those are very strong runners and dead solid reliable in long term service.
All of the reed-valve top and rear handle saws are pretty much "turds", but decent grunt and pretty reliable.
The CS-355T is a really nice unit.
The CS-370/400's are excellent mid-range saws with plenty of '"grunt" for the cc's, and also very well built and rock solid in long term service. My CS-370's are my "go-to" saws here for small jobs around the properties.
The CS-670's are just OK, the CS-800 is far from a "professional" model. I guess they have decent potential "ported" but in stock form lackluster for upper mid-range and top end power. If you own a Husqvarna 268XP/272XP/372XP you'll NEVER find yourself reaching for either of the Echo's.
The CS-590, 600P and 620P's are excellent. They have a broad/smooth/flat power curve and pull hard at higher RPM's combined with plenty of "grunt". This allows them to manage larger bars with decent authority for 60cc saws. They will also not clog up so you can cross-cut/noodle large pieces into smaller ones to manage them to the splitter. Below are pics of a HUGE Maple and Beach tree that I whittled down to size with my CS-590, making dozens of cross-cuts to get the huge pieces manageable.....it never grumbled once..........Cliff
View attachment 930621View attachment 930622