I exploited the CS-6700, CS-670's and CS-800 years before Echo came up with the CS-590/600/620 series. My intentions are NOT to come on here and bust on brands or models some folks are well vested in, proud of them, and/or really like them. Just putting up usable and accurate information as I know it to be from direct testing, so here goes.
Nothing at all wrong with the 670/680/800's but they lack professional features, like an inboard clutch and clutch driven oiler. The 800 also has a "goofy" rubber plug to remove to get to the mixture screws and didn't use the excellent round automotive style filter many other Echo saws are outfitted with.
All of them had decent power (torque), and cut OK. I found that none of them "lugged" all that well despite having decent low to mid-range power. They simply "fall" out of the good power easily, so I found myself keeping the rakers high to avoid the chains getting a real big bite in the cut. Once you realize the limitations and capabilities they're a fine saws, built like tanks and I'm sure they'll last many years if one keeps them in good tune and regular maintenance.
In comparison to a Husky Pro saw of equal cc, like my 268XP, there really is no comparison between it and the CS-6700/670's. It will out-cut them with ease and flat out SCREAMS at high rpms and pulls down pretty hard pushing it hard in big wood as well. My 268XP free revs "four stroking" nicely around 13,700rpms. Couldn't get any of the big Echo's even near that RPM leaning them out and trying to lean them up resulted in instant stalling against the clutch when you "push" them really hard. I also replaced the P/C on one of them and noticed some "odd" looking porting. I've seen a few threads here and there where some folks were able to make huge gains with those P/C's with specific porting and tight squish. Even so I'm not into all that and stick with stock saws with at most limiter caps removed and maybe opening up restrictive mufflers if/as needed. So from what I've seen with those saws, they are "older" designs and just OK.
The CS-590/600/620 series in contrast have excellent features, inboard clutch, clutch driven oiler, excellent anti-vibe, improved "ergonomics", and broad/smooth power curve with much greater power in the upper end of the RPM range. The power curve is strong enough and broad enough that you can push them pretty hard and not stall against the clutch. Just yesterday I but off a dozen Ash stumps down to ground level with my CS-590 and it never grumbled once no matter how hard I pushed it. It was outfitted with a brand new Oregon semi-chisel chain which really helped that scenario.
The CS-620PW that I purchased about a year or so ago is a flat "home-run" for a 60cc saw. Very strong power and I've ran bars on it as long as 28" without skip-tooth chains. It actually does quite well with a bar that big for a 60cc saw, but is a real screamer with a 20" bar and not too bad at all with a 24" bar on it. I'm hoping Echo at some point throws some of that deal into a 70-75cc chassis. When they do it will obsolete the CS-670/680's and probably the 800's as well........FWIW......Cliff
