Unless you're writing >20GB a day to your drive, you don't have to worry about longevity. As for keeping its speed? It's true that SSDs slow down with use, but even at their slowest, they are vastly quicker than even the fastest of hard drives. I would say stick with the SSD.
Which SSD do you have, and is it having any problems?
cjl is right, overall an SSD is going to be faster and more reliable than any HDD. The 5 year lifetime at 20GB of writing/day is getting pretty close to the life expectancy of a hard drive. If you're looking for a guarantee that your data will be safe beyond that point then I suspect you're going to be disappointed.
The fastest HDD (in terms of access times) you can without going to expensive Enterprise drives would be a WD Velociraptor.
I have the GSkill titan 128gig ssd. I have been reading on their forums that they only have a 8-10,000 writes per sector limit. Several users have reported the drive hanging on boot (which it is now doing for me about half the time I boot it up) and slowing down to a crawl.
apparently Gskill is not updating the firmware for them at all.
Yeah I have those problems too. I have several laptops with different makes - I do photoshoot and video capture with my laptops. What I did I have an external hdd to put my files on. I have tried SSD before and lots of problems came up so I stick to what I have tried best - It is not the fastest thought but for me it works and quite practical.
I have the GSkill titan 128gig ssd. I have been reading on their forums that they only have a 8-10,000 writes per sector limit.
I know nothing about these drives, but I'm a little skeptical about that claim. The 8-10,000 writes sounds like the wear limit for each individual flash memory block, but the firmware in most SSDs I've read about distributes writes across the entire device so that no one sector will wear out first. 8,000 writes is a lot when it's spread evenly across the device - for example if you were to completely write every sector on the drive once a day then the drive would still last for over 20 years.