mSATA SSD ARE SATA3! And YES, well worth the money.
The limiting factor will be your motherboard. If it supports SATA3, that's what mSATA would be.
Bottom line: ANY SSD you'd get (SATA or mSATA, SATA2 or SATA3) will be way faster than any HDD.
HDDs don't even come close to saturating either SATA bandwidth.
Thanks! That was fast. Thank you also for clearing up the misunderstanding between mSATA and SATA3. One last question. If I am on somewhat of a budget do I need the best SSD or will any outweigh an HDD. I was just going to get one with at least 120 gb of storage for my boot files then use my HDD for everything else. Is it necessary to buy the nicest one?