Hi Dan, you are correct, now and then batch lots of production springs will vary and we may update the site, however Black/Blue has always been the same. The black/ Green was adjusted slightly for a different batch at one point.
I just happened in and noticed your post. I came here actually to post a new updated list of primary springs, since we have a couple new ones as of today.
Some new springs were developed based on demand from people testing ...many have claimed to have found that lower engagement springs were only making more lag and wanted stock like engagement....but a replacement for the stock primary spring. The stock primary spring has had a few issues. It is long, but it is not simply the fact that it is long, it is long "with a lot of coils of very small wire" and as some noticed, distorts quite a bit at full compression. Not to mention fairly tight and sometimes rough spring pockets.
We now offer a stock like engagement spring, as well as a new even higher rpm engagement spring for racer types that requested it.
Up to this point, it seems the most popular ones for sidewinder are Black/Red, Black/Blue, Black/Green, ..with black green most popular. We have now expanded that and time will tell of course.
Here is the updated list with more new options.
http://www.daltonindustries.com/product_detail.php?product_id=72