Mark,
I didn't answer your question, sorry. The aluminum is a bit stiffer than the steel but it's hardly noticeable, so I would say Yes they are about as stiff. The weight savings makes the Aluminum a must have for us due to the terrain where we tend to ride and having to chase you little people up hills. I also had them build it compact and now I have the bike under 32 pounds with all tandem approved parts. The new Rolf wheels are very solid and a great upgrade.