Ok, sorry if I made it sound complicated--it's hard to know how much info people are looking for, so, when I can, I usually try to provide more complete answers. Hopefully to avoid someone going out and buying something, then being surprised.
The short answer to your question is your new internal drive, if it's 6Gb/s, is a SATA III drive, not SATA II.
Regardless, it'll work, and your system will *not* slow down that drive, despite it's higher rated speed. That rating will offer no real-world advantage with that drive.