What are the differences ?

Possibly - but you will have to do some listening to your favorite LPs! Sapphire is certainly stiffer than aluminum! Maybe more low-level detail?

The problem in answering this question is that the cartridge probably sounded ratty when you last listened to it, which is why you sent it in for a rebuild, so it may be hard to remember exactly how it sounded compared to the new one.  That said, I had SS work on 2 cartridges for me and I was very pleased with the sound when I got them back.  I had a different situation in that Peter only replaced the stylus and not the cantilever on mine.  I didn't ask him to do this, I just asked him to do what you think best.  I don't think Peter would have replaced the cantilever on yours if he didn't feel it was the best choice.  My guess is you will install it and be very pleasantly surprised.  

I didn't send the cartridge to soundsmith because of wear but because while mounting it onto my turntable I destroyed the cantilever . Having said that it was probably time for a retip anyhow as I've been using the cartridge for 12 years . 
I asked soundsmith if changing the material of the cantilever from aluminum to shappire would give me better sound he said no , that it would probably track better but that the cartridge would sound as it used to .