Funny to see this. I've been pumping St. Croix combinations through the search feature here looking for info and opinions. Haven't found much except a generally rather positive opinion of St. Croix's in general. Recently got it in my head to build a rod and started looking at blanks.
My favorite rod isn't the 7'6" 3-weight that I though it was. It's a 7' 2/3-weight Ct. Croix Imperial. So I was thinking to go this route with a new blank to build.
Here's the St. Croix Home page: St. Croix Rods - Fishing Rods, Fly Fishing Rods, Saltwater Fishing Rods, Rod Manufacturer
Looks like the Premiers were made form "Premium-quality SCII graphite", which woulds be around the same as the Rio Santo fly rods they are currently selling. Looks like the Premiers are just Spinning / casting rods right now.
Anyhow, if that blank is rated for a 5-weight line, and you have a decent line on it, you should be 'okay' at minimum.
Don't know the Premier rod first hand, so the above is what I do know about St.croix in general. Reels, I have no experience with with St. Croix reels, so my fingers are staying still on that subject.