First, you are correct, for equally sized drives an SLC drive would last 10 to 20 times as long as an MLC drive. However, using any SSD near capacity without TRIM in a heavy-load environment (which you may be doing) will send it to an early grave.
I started working on a post to address your (very good) questions. I'm learning more myself as I write it. It's kind of lengthy and complicated, so I need more time. If you can wait, I plan to post it by sometime tomorrow night. In a previous post
I talked in generalities about using over-provisioning to extend the life of SSDs. My next post will get into the numbers and mechanics behind determining endurance and how (specifically) TRIM and over-provisioning are incredibly important to the life of a drive used in a demanding application such as yours.
If you read this before I post tomorrow, could you provide me with the amount of data you are storing on your drive? How much you plan to store? And, if you know, what approximate percentage of the data is static (rarely changing)?