Hi robotrobbie, did you already found out about the SATA II (300) or III (600)?
I also bought the 5750G for my girlfriend last year and i have 2 SSD's at home (1 is SATA II, the other is III) and i like to put 1 in her laptop.
I checked the specifications with Speccy (a program from Piriform, maker of Ccleaner, totally legit) and it told me the interface/connector is only SATA II. It didn't give me information about the optical drive type of SATA though.
If you want to put an SSD in the HDD bay, you'll need to remove 2 pieces of plastic that prevent your SSD from plugging in all the way (because unlike normal HDD's, the SSD casing completely covers the SATA connectors). I wouldn't recommend this as long that your laptop is still covered by warranty.
Pretty stupid of Acer not to make a decent space for an SSD and even more stupid to use the SATA II for the HDD bay. That's also why some of the 5750G's (MFG Date before 1104) were recalled.
So the only option for me seems to be an optical bay caddy. I'm looking for one now and i'm pretty sure when I'll plug it in, Speccy will tell me what kind of SATA it connects to.
I know this thread is 7 months old but i still like to hear what you found out since then...