The Cardas bananas are made from eutectic Brass with Rhdium over Silver plating. Be careful with system synergy as the brass/silver combination can make a very strong solid-state system sound sterile. These could be good for a very soft or laid-back system.
Ultimately, I think Futurech is superior for metallurgy. The "pure copper" Furutech bananas (CF-202 and FT-212) may have an internal spring to help tension on the banana plug fit. Not sure how this will fit in the speaker binding post as the fit may be somewhat loose (depending).
The Furutech copper alloy bananas are a stiffer material (FP-200B and FP-202). The FP-200B can be flexed open more to provide a tighter fit into the speaker binding post (if needed).
The Furutechs are available in both rhodium and gold plated.