I am not sure what you meant by the 3/6 SATA? I am going to guess you meant SATA II (3 Gbps) and SATA III (6 Gbps). The 9,1 will destroy a 5,1 on benchmarks. The better question is, are you satisfied. Plenty of SSDs that are SATA II will give some nice speed as well as upping the RAM. The tasks would obviously be faster on a new one, but a 5,1 can more than cope with those upgrades!
If you put an SSD and max out the RAM in a 5,1, it will be more than adequate for those tasks. I have a family member who has the aluminum 13" MacBook from Fall 2008, a friend who has the 13" MBP from mid-2009, and I have the most recent model (mid-2012). When those two machines had an SSD (3Gbps), they felt faster for most basic tasks than my computer (when it had a spinning hard drive). For CPU usage, if you're using tasks that can take advantage of the newer CPU, the new machine will smoke the old ones.
Still, like I said - for general, intermedia tasks, those are more than adequate machines with a few upgrades.