i can give you a bit of advice here.
i was lucky enough to try all the 04 125's except the husky at the beggining of the year.
I loved the SX, like you said, it has an awesome little engine but i felt the suspension needed a lot of work. i liked the ergo's on it. felt very light and flickable, which was mainly down to the rad shrouds being so inwards.overall i was impressed but the potential sus work that was needed put me off.
The CR.....Sh!t. complete rubbish, i was being smoked on the straights by 85cc's. akward feeling bike with no power. but the components like always are well made on hondas. but wouldn't touch one again.
The yam. decent engine, good top end i thought with a reasonable bottom. the suspension was superb and soaked up the bumps beautifully. a very forgiving bike.
it rode well but after 20 minutes it looked 5 years old. doesn't scrub up well. minor detail though.
The Rm surprised me, i've never thought much of suzuki to be honest but this bike ripped it up. great all round engine. nothing that was overly powerful but a good balanced range that i enjoyed.
the suspension was good, minor adjustment had it perfect for me. it's a great looking bike.
the only fault was it feels a bit chunky and because of that made it feel heavy.
apart from that, great bike.
the KX, as you probably guessed was my fave.
stock, it was awesome. the bottome end is so sharp it pulls your hands off of your wrists. the mid and top end just click with one another and the power from the mid range is instant. could't fault the engine. kawasaki have excelled here.
the suspension is great too, minor adjustments and it soaked up everything you could throw at it and it was the easiest bike to turn, it just carvs the corners perfectly and never trys to jump out of line going high speed.
the ergo's i loved, super slim and small and with me being 6'2" tall i felt so in control of the bike, it was like riding a bmx with and engine. super light and flickable.
so, there you have it. obviously i am biased and i love my KX but i've given you my honest 1st impressions of all the bikes. the kx has held up well so far, no problems yet...touch wood.
good luck.
welcome back to the wonderful world of the 2 strokes.