I can't really comment on the 5.6x57 case neck thickness as I've never seen one.

However I did notice the 6.5x57 RWS cases have quite a thick neck when compared to the neck thickness of a 8mm mauser cases I've used to neck down which were made by winchester or Remmingtion ?
I also noted that the 7mm mauser cases made by RWS had a neck thickness comparable to the factory 6.5x57 cases that I had picked up and worked well with no reloading or sizing problems during the necking up to .30 cal and back down to 6.5mm.

I'm not saying that the difference in neck thickness is huge, but it was enough that the remmington brass would not resize in my dies when all the other stuff would?

Just a quirk I have come across in my time reloading for it.

FatBoy,
I'll post some loads for it when I can get time to Chrono them unless you're just after starting loads? I also found that the data on http://www.reloadersnest.com/frontpage.asp?CaliberID=113 and http://www.accuratereloading.com/6557.html were a good starting point.

Cheers

Red