Trim is irrelevant. You are not going to be using this machine as a "daily driver" to even come close to wearing out the disk. two, when you take the drive out and put it in a new machine, you can run it then. three, with small SSD drives in the $20 range, its hardly a consideration. four, most drives now do trim on their own. At least the name-brand ones are supposed to.
the SIL3512 is a "raid" chip. it can be re-flashed to normal sata, but it would be a bit of a hassle, imho. IIRC you want the SIL3511.
I have a few of those cards, and they work fine. I would still get the sata2 card. there is an edge-case with sata3 drives. some do not work with sata1 controllers. its troublesome with cheaper drives.
Once men turned their thinking over to machines in the hope that this would set them free. But that only permitted other men with machines to enslave them. - Reverend Mother Gaius Helen Mohiam