The SolidSteel tables are real nice, I have two 5.5 and an amp stand. They're not the absolute best performers but are excellent value for the money. If you want to improve performance you can fill with sand and/or lead shot, but it is a pain since the passageways are small. You can also replace the shelves, which are the weak link, with something better. As I undertand it the 6 series is similar in frame construction but uses a better shelf. One minor detail, somewhere in the last few years they changed the dimensions, the newer models are slightly bigger and the shelf spacing varies. I have one from the early 90's and it has the same spacing between all shelves. I bought a used, but newer 5.5 about a year ago, it has a good sized lower shelf to accomodate a fairly large amp. The top plate is also bigger to accomodate slightly larger turntables. Construction quality appears unchanged. Biggest drawback is they are welded and therefore bulky to ship.
