I have been looking into intel SRT recently. Essentially it boosts the things you do most on the drive, but leaves everything else at HDD speeds. So it can give you near SSD boot times after a couple of boots, and the same thing with programs. But it won't give you full SSD speeds even in these things, and does little for seldom used programs or your data.
A straight forward SSD boot drive will make everything you can fit on it much faster, but obviously does nothing for any of the files on the HDD.
I'm moving to SSD myself, and my feeling is that it's a price/capacity issue for the most part. If you can afford an SSD large enough to take all your programs then get one as a boot drive and a separate HDD. It is by far the fastest way to go. If you feel that you need more capacity than you can afford in an SSD, then either get a smaller SSD for boot only and keep most programs on the HDD or use it to SRT the HDD. It's really up to your own preference in that situation.