Mike,
Western red cedar, of any age, has never been a problem for us using regular RS stains. We have stained a lot of cedar decks over the years without problem, and some white cedar fences.
Regular RS "mellows" out in coloring on most woods in about a week.
It is the very old growth redwood, from ancient trees, that turns black, with regular RS. And the result is immediate. Black as coal, as the regular RS seems to push up the natural tannins in the redwood. I am told that it ages to a regular stain color, but cannot vouch or bet on it as I have to satisfy customers.
AFAIK, the difference between the two is solvents.
Just do a test spot on the redwood siding. It is very obvious, and real quick. Call Peirce with any questions, as his contractors deal with redwood a lot more than we do.