SATA3 SSD on SATA2 port? huge difference?
 

Just bought an used Adata S511 60GB (SATA3) to replace my old 80GB HD that read at 45MB/s, the new speed is like day and night, I love it, but would it improve much more if I get a SATA3 PCI-E card? like startup speed, shutdown speed, application startup speed etc.

SSD will always be faster than HDD, but I don't recommend PCI-E Sata3 cards simply because there is no good yet affordable solution. Anything that can push true SATA3 speeds is so expensive (server solutions) that you might just replace a mobo with Sandy Bridge native SATA3.

On a Sata2 port, you would max out at aroud 2xxMBps. Still light year ahead of regular HDD.

Depends on the SSD

In the case of the A-Data, yes, it would need SATA3 to run at full potential.

Still faster than a mechanical drive of course.

Probably not worth buying a card though, since the controller it will be based on (Marvell most likely, or JMicron) will not be as fast as a proper SATA3 controller on an Intel or AMD chipset. It might be a bit faster than what you have, but I doubt it would be worth the time or money go bother. Just wait for your next upgrade to enjoy the full potential of your drive.