Not a single word about TRIM? (didn't read through everything, apologies if I missed something)
If it hasn't changed since last time I checked there is no card that can do TRIM on RAID array. Having no TRIM at all can, in time, easily outweigh any benefits of RAID and thus perform much slower than even a single drive.
You could probably do some hacks to improve non-TRIM performance such as ensuring that some (TRIMmed) space will never be used - i.e. before making the array, make sure that everything is TRIMmed and leave x % of the array unused at all times (by making sure that you don't even partition x % of the array for instance). That will save some space for the controller to juggle data around and should improve write speeds significantly when the array gets full.
But a better solution in many cases is simply to use the two drives as is. For instance one for the OS and one for applications. Especially with the newer and faster SSDs coming, pure bandwidth isn't the whole picture and with Intel G3 around the corner the use of SSD-raid should, for most people, not be that appealing.
But really, I'd recommend a single large SSD for most of the cases. A 160 GB drive is often more or less two 80 GB drives in the same package anyway so you could say that you already are running them in RAID 0 in some sense (other bottlenecks take place (the controller for one) but write speed for the G2 160 GB is much better than the write speed for the G2 80 GB).
And thats probably the main reason for why the budget-drives are smaller and why the smallest G3-M drive will be 160 GB and not 80 GB and why there is no X25-M 40 GB. They can't make smaller drives in the same performance-league as the larger ones.
Please correct me if I'm wrong, I might be a bit outdated on the subject but I use full disk encryption on my G2 80 GB so I sure now how devastating the lack of TRIM can be for performance when the drive gets full.