More than speed of players, it's the agility and dynamism (players from your team + cpu running moving all too fast)
To be honest i don't have difficulty to score or more, to win at all in both PES6 and WE10le against CPU. I remember scored 3 or 4 goal 5 stars difficulty directly the first time i tried as i didn't know WE10LE it existed on the past so i wanted to try it. To me it's the same as PES 6 but faster, now i won't say anything bad regarding the game as i didn't really played it a lot, just a matter of feeling, a bad Pes6 taste on my mouth the first time i tried it. But i will give it his chance as people said often it's not a bad version

Now about WE10 i made a league with friends on it and it's probably the version i hated the most, his Occidental young brother can be fun with small teams (we also did a league on it, we created a bunch of small teams over Others C > it was fun) but WE10 is dead for me i'm still searching where the midfilders are on the pitch.
PES 6 has some potential and i owned the Xbox 360 version, there was inertia, the game was slower, it's harder to do everything etc. and it's fun as scoring needs at least a little more concentration. That f****d up potential (freedom to move etc. but all is tainted in red by bugs, counter, success rate level etc.). is the main reason why i hate PES 6 ps2 and didn't played on that version neither on PC. All that potential trowed by the window just to please to a bigger crowd : same as Efootball but PES name was iconic and people brought it eyes close same as myself.
Sad that the 360 version got an edit mode cut in half otherwise i would have really loved it if it was on PC. You should try it if Xenia run on your PC and you'll see : even animations are much more natural than PES 2008 on the same console/generation. Now there's people who don't like it, matter of taste, but like Efootball when the game have bad reputation due to X stuffs (out too soon) most of people play just to check how bad the game is, not simply testing it for real. Cyberpunk for example became a great game and the Dlc give it really a second breath. But still the name, the story behind and the sticker on the game's image "bad for eternity" lol even if the game change totally with years and patches.
Now back to retro PS2 talk :
And yes PES 5 is more dynamic that's true but players agility and moving with the ball is way slower. Passing too, but defenders are faster yes, probably because they don't have the ball and it's more marked on PES5 the with/without the ball speed.
Speed doesn't really bother me if the game is good, and still feeling human, of course there's some acceptance limits lol.
But PES5 isn't the faster PES in comparison to the 4 or WE10). I ain't a fan of WE9LE neither. it's not an improved but a different PES 5 version. And WE9 is probably the most defensive PES you can found with PES1 or WE5FE. Then, i don't search a total simulation, but an active football balanced like Seabass described the series named it "action football".
If you want the game i purposed you can ask me on PM, i can upload at least JLWE10 (the Jl2007 is easy to found)
Now to be honest, i said they're a better PES6 version but it's still not part of my favourites gameplay, vanilla of course. WE2008, PES5, WE9 and JLWE2008 are my top 4, i'll add WE5FE appart as it's a very different type of gameplay but i really love it. Then there's WE7 and WE7i, WE8LE, and the games i mentionned.
Mmmhh i truely believe than the korean version are corrected to suit to korean player, which make it another game for those people. Both Korean version was out very late and don't even get transfers you can found in game's out in april-june with J-league : i suppose the game is directly modded from PES 6, while the others are a succession of enhancements and plays differently : i talk about WE9LE case as i know that one better for example.
JLWE2007 AI should be more adequate as it's the closer database version of PES6 serie with updated transfers.
Ps: sorry for the long read, passion is my second name