You will buy a new hard drive before you wear out the SSD. That said, when you set your save path, it will save the files directly to whatever disk that path is located at.
You're wrong. So, so wrong.
Since I bought my SSD I've download more than 1,5 TB. I've been using BitTorrent and Vuze as torrent clients.
Today I was doing some research on SSD wear and through the software showed on the image attached to this post I found that when I started Vuze, downloading at 500 KB/s, the same speed of writing was being made on my SSD, even though all downloads are set to my storage HDDs. When I stop downloading, the writings stops too. This is obviously the client cache, which is is small, that uses the SSD. Not only the real time readings while Vuze is running prove this, but also the lifetime writings of 1,88 TB, which totally corresponds to the more than 1,5 TB I downloaded since the SSD upgrade.
So, yes, your torrent client wears not only your HDDs for storing, but equally wears your SSD because of the cache (little parts of the files are first stored in a cache in the SSD, then transfered to its destination folder, being in this case, another drive).
I didn't find any option within the client to change this. I'll try to uninstall the client from the SSD and install in the HDD. This might change the scenario.