Newer SSD's such as the Vertex 2 are spec'd at 250+ MB/s for write. IMO, the write speed issue for SSD's are gone, there's no reason why you shouldn't plunge now.
If you're talking about just read speeds, I think the Corsair SATAIII SSD's have a read of 330 MB/s or something crazy like that, but it drops to 280~MB/s on SATAII, so throughput isn't the only difference.