So you're saying one SSD is better than two no?
It will depend on the drives being compared.
For example, lets say your 80GB Intel's can generate 70MB/s for random access performance (likely the single disk performance, as random access is
not doubled as sequential access is in real world testing), and a newer SSD you might be looking at, even though it's a SATA III model, only generates 50MB/s, then your existing disks would be faster.
So the best thing to do IMO, is take a look at independent reviews of the drive's you're interested in, and compare them to what you already have for random access throughputs.
Now there are RAID levels that do improve random access performance, but that means 10 if you plan to use Disk Utility, or a proper hardware RAID controller, in which RAID 5 would not only become an alternative, but is actually faster than 10 for both sequential and random access throughputs (why relational databases have shifted from 10 to 5 in the last 5 years or so).
Unfortunately, if you decided to go with a RAID 5 implementation, and do a lot of writes to that volume, then you'd want to use SLC based SSD's due to the higher write cycles that result from the parity writes (won't really be an issue if your usage is predominately reads = less expensive MLC based drives would be acceptable in that case).
