The Intel® SRT (Smart Response Technology) is really designed for SSD smaller then 64GB. The only way to use a larger SSD is to partition it down to 64GB or as a drive and then the rest left over as a second drive. So JohnnyLucky is the expert here and may have some additional information to help you on the set up for best performance for your needs.
There is a lot of misunderstanding about caching. Intel developed caching for clients and businesses that could not afford a large capacity ssd. Back when the concept was on the drawing board, Intel hoped clients and businesses would purchase a small 10Gb or 20GB for about $100.00. Microsoft Windows 7 and all software applications would remain on hard disk drives. The cache only produced a minor boost in performance. Intel hoped that once clients saw the slight performance boost they might be inclined to purchase a larger ssd.
Intel also researched the size of the cache. Intel determined that a 60GB ssd was the point where it made no sense to use the ssd as a cache for a hard drive. Instead if you have a 60GB or larger capacity ssd, then Windows 7 and software applications should be installed on the ssd to take full advantage of the ssd capabilities.
Since you are thinking of purchasing a 120GB ssd, it makes more sense to install Windows 7 and your software applications on the ssd. The ssd performance boost is much higher than the hard disk drive performance increase.
Windows 7 will use up a just a little over 21GB leaving plenty of room for software applications.
I do not know if you are a gamer but I hope you know that an ssd will not improve actual game play and it will not improve FPS. The only thing that happens is that the game will launch faster and levels, maps, or charts will load faster. If you participate in online gaming, then the ssd will not improve anything. You'll still be at the mercy of your Internet Service Provider.
A few weeks ago Tom's Hardware published "SSD Performance In Crysis 2, World Of Warcraft, And Civilization V". It is an analysis of ssd's and gameplay. Here is the link:
I would think the benefit of setting up a smaller (40GB or so) SSD for caching with the SRT system would be worth the small investment compared to the high price of a 120GB or 240GB SSD to use alone, or going straight off of the existing HDD would it not? From a cost/benefit point of view, it would give you a decent lift in performance (load times) for a minimal cost. Obviously purchasing a 240GB SSD and putting your OS and all of your games/programs on there would be the best option, but if one doesn't have $600 to spend on a SSD, is the SRT caching not a decent upgrade for your money?
I did not want to pay a lot of money for an ssd either. I purchased a Kingston ssdNOW 100V+ 96GB ssd when newegg had it on sale for $99.99 and free shipping. They periodically repeat the sale. Just have to be patient and wait.
The 96Gb was more than enough for Windows 7 Pro 64, all of my Adobe photo editing applications, web publishing software, Microsoft Office Suite, and some additional software and utilities. The grand total came out to a little over 31GB and I still have over 60GB of unused space. Games are a bit different. You could probably load a couple of your favorite games on the ssd. If you have a lot of games you could store them on a hard disk. Swapping games between the ssd and the hard drive is easy.
The problem with ssd caching (Intel SRT) is that it only produces a small hard drive performance boost. Might as well use an ssd to it's full potential instead of settling for something less.
I have the Intel® Desktop board DZ68BD and a Intel 320 80GB drive; I run it as boot drive to get the best performance. Will the Intel SRT (Smart Response Technology) give you a performance boost with a smaller SSD? yes it will. With that performance increase reach the level of a SSD as a boot drive? no it won't.