I would immediately rule out option two. Although in theory you could get double the bandwidth* with two drives (similar to how RAID0 can improve performance), it would probably be better to get a single SSD with 80GB. This is because SSDs tend to be faster the more free space that is available (as mentioned in an earlier answer).
SSDs excel at random read/write performance, and usually perform well at sequential read/write. You would probably overall sacrifice the former, for a potential improvement to the latter (with two 40GB SSDs rather than a single 80GB SSD).
*but only when reading to or writing from both drives at the same time
These are just speculations, but referring to the configurations in the question: (2) should provide better performance than (1), due to the potential for increased bandwidth and parallel access. But it’s also worth considering configuration (3): a single 80GB SSD for OS/apps. (3) would obviously be preferable to (1) due to the larger capacity (which leads to better random write performance). (2) should offer better sequential read/write speeds than (3), e.g., when copying a large file from one SSD to the other. I’d also expect random read performance to be slightly better for (2) than (3) (when both the OS and an application simultaneously need to access the drives/drive).
But (3) may offer better random write performance than (2), because one large drive is preferable to two smaller drives - the more free space the better. (3) should also be slightly cheaper than (2). I’d also say that random write performance is the critical advantage of a good SSD versus a HDD; it’s a much more common operation than copying a large file between two SSDs. So I’d buy the option with the best random write performance (at a reasonably cost). But obviously benchmarking is needed to verify my hunch...