No experience with the SAR-3, but I do have a .223 Norinco and a Romak-2 (Thumbhole SAR-2 in 5.45).
The .223 Norinco shoots great. No recoil, a little less accurate than my AR. Absolutely devours the cheap steel case stuff without a hitch. I like the fit and finish of the Norinco a bit better than the SAR as well. Mags aren't as easy to find as some guns, but they're around $30 eash or so, and are steel of typical AK design and construction. They are around, so they aren't that rare. It would only cost you a bit more than the SAR, and I think it's a better gun.
My Romak-2 I fell in love with once I shot it. It is also an accurate gun, also just shy of AR performance. Low recoil, fun to shoot, and mags are dirt cheap. I am waiting on arrival of some US parts to get my PG conversion going. I have to throw in with the others that 5.45 is a great cartridge for the AK. I enjoy my 7.62x39 ones, but I wish I had discovered the 5.45 earlier. It's a pretty cool gun.
The Norinco is a slightly heavier gun than the SAR. It has a thicker barrel, and most of the metal is thicker as well. It's the same construction as your 56 was, so just picture that with no recoil, and better accuracy. The mag cost is the only drawback, and that's not too bad.
I'd love to advise you on the SAR-3, but I haven't ever shot one, let alone owned one. All stories seem to hint that the mags are problematic, unless you go with Wieger mags, which are probably a bit cheaper than Norincos. There are some concerns as to the geometry of the SAR hammer since it's designed for a 39mm length, an the .223 is 45mm. Seems you may ahve to whittle on that some as well. Quite frankly I think the SAR-3 is just not quite right. That's why I've stuck with the Norinco and not bought one of the SARs.
If I could only have one AK for real use, I'd go with a .223 Norinco in a heartbeat. Good caliber, good set-up for that caliber, good quality, good accuracy, great reliability. There is an AR mag conversion available. Iv'e shot a Norinco with the mag adapter on it and it worked great. Kinda neat, but I personally like the AK mag design, so I never bothered.
Ross