Spread out your purchases but get your SSD last of all.
By then you will get more for your money and sata 3.0 SSD's may be out about that time and you may then be getting 600mb/s read and 500mb/s writes which should help with creating/copying those ISO's etc.
lol, but that would mean i would need a new motherboard too! 300mb/s is the bandwidth cap on Sata2 right?