There are quite a few SSD's planned for the market. Finding them and hence being able to buy them are another story. You've done well to even find a 4GB / ATA unit.
The 4GB is a bit small but may still work. You want to put your OS on the SSD, or at least the system cache (paging & such) there.
Samsung has announced a 16GB unit; such a size would fit win/XP without question. The read and write speeds are similar to what you quoted. Apacer is developing a 32GB sata unit with 100MB/s read/write speeds; 3.5" form factor too so it's a drop-in replacement. That product ought to displace SAS units, i.e. very high performance. Ritek, Pretec and PQY have also announced SSD's.
And of course, you will want to layer your hierarchy of storage devices. A Raptor may not be the most cost effective backup to an SSD. You may want to consider the Hitachi 1TB or the Seagate 750GB, since both have immense capacity are actually very close to the Raptor in terms of performance. There is also some coolness factor too when you mention a 32GB SSD *and* 2TB in RAID.
Remember that those speeds are the sequential read/write times. Readyboost needs fast random read/write.
Having said that, Readyboost is designed for removable drives such as USB sticks or maybe CF. This is an ATA drive so you can't use it, even if you get some kind of USB enclosure (I think). However, you should be able to get the same results by simply assigning the whole drive as your pagefile.