From what I remember, the altos and tenors have a pretty normal linkage design for C#, so if it feels stiff (and I found new Borganis to feel a bit stiff in general) then it can most likely be improved by adjusting the spring (possibly both springs).
The problem I mentioned is specific to Borgani sopranos (possibly some other brands too). Even with a relatively light spring to the C# key, the lever needs a strong (or overly tensioned) spring to close the key reliably, or at all. This is to do with the design of the linkage. You can see a photo of it on my website, review of a Borgani gold plated soprano (one before last photo) http://www.nitailevi.com/reviews/sop_sax/borgani/borgani_sop24k.htm
The problem is the direction of the force. At closed position, the force from the lever is not in the direction that closes the key best, so a lot of it goes to waste. Imagine a big square box that has walls on both sides, so you can push and pull it only forwards and backwards. Put your arms up and try to push it forward, you need a certain amount of force to do that. Now stand in an angle to the box and push it forward but also towards the blocking wall. The box would still move forward, but you need a lot more energy (force) to move it the same as before. Use the same force and it moves less. This is the problem with the key.
The design can be improved, unfortunately with some damage to the finish in that luckily almost invisible area (the finish seems to be silver, then gold, then clear lacquer). My friend who owns this soprano chose to have it done and accepted the small finish wear, and never regretted it. Every one of the approx ten sopranos I've seen had this issue.
Sorry for this long winded post, but this problem really gets to me.......