Crucial drives get far better ratings than OCZ drives, but IMO 64GB is not enough.
I would research the reliability of those OCZ drives before buying, or at least buy from somewhere with good support, someone that won't make you immediately send it back to the manufacturer for replacement.
Don't buy anything smaller that 100 or 120. I have a 64 and it only has enough space for 2 games and nothing else. I use Steam, which will not allow you to place games onto other drivers. I am currently saving to replace my 64 with a larger drive.
Oh yeah, by the way I love my SSD drive. I would never go back to a standard drive. So much quicker.
If you are planning to purchase a motherboard with SATA III (6 Gb/s) capability, then it would be appropriate to purchase a solid state drive with SATA III (6 Gb/s) capability. If you purchase a SATA III (6 Gb/s) ssd now it will work quite well when connected to a SATA II (3 Gb/s) port on your current motherboard. No problem.
If I could only choose one of the 3 ssd's you listed, then I would purchase the Crucial C300. However, it would be a 80GB drive. The extra capacity will come in handy.
For the diff in performance between the C300 and a SF1200 SataII SSD, I'd go for the Size. You will not see a big diff in performace on a day-to-day basis, But with more space, you can put more on it. @ same size, yes C300 (Not a lover of the C300).
A 100 Gig SFxxx SSD, Be it Sata II or Sata III, is going to be a better choice than a 64 Gig Sata III
Not my choice in brand, but 100 gigs right @ $200 http://www.newegg.com/Product/Product.aspx?Item=N82E168...
or 120 Gigs @ $203 - May be slower, but almost 2x a 64 gig drive, and as I indicated, Not a BIG diff in day-to-day performance. Remember whats NOT on the SSD will so NO benefit. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
There is one other option. If it is going to be a while before you purchase a new motherboard you may want to delay purchasing a new ssd. We've had quite a few new ssd's introduced recently. We are now approaching the Summer lull. We know that another batch of new ssd's will be introduced in the Fall in time for the winter holidays. If you can wait you could do one of two things. First you might be able to purchase an existing ssd for less. Second you might be able to purchase a brand new ssd with a few more features or improvements.