I'm contemplating biting the bullet for an ssd drive in a server, obviously I know it will be MUCH faster than a regular 7200rpm sata2 3gbps drive.
The nice thing about ssd's is often they post the read/write speed but that info isn't available for sata's so I'm just curious to know what a typical read/write speed would be for a seagate 120gb 7200rpm drive. I know it fluctuates from manufacturer and model series but I'm just looking for a guestimate.
The performance of a drive depends on many factors and simply comparing vendor claims for maximum transfer rates will not tell you the whole picture.
However to answer your specific question the 120GB 7.2K SATA drive you refer to has a sustained read\write transfer rate (for large sequential IO) somewhere in the region of 50-70Meg/sec. A current generation 7.2K 2.5" SATA drive will come close to double that (e.g. the Seagate Momentus 7200.4 laptop drive averages close to 100Meg/sec). Current generation 10K and 15K SAS drives should be able to sustain 50-100% faster sequential rates depending on model and interface. The 200-400Meg/sec transfer rates claimed for current generation SATA SSD's are very fast but they are not the SSD's real strength.
For a server environment things like random IO and the ability to handle large IO request queue depths is generally more important. A 7.2K SATA hard disk will have read\write latencies in the range of 8-15ms and can handle about 70 discrete random read\write IO operations a second. SSD's have latencies measured in microseconds (e.g. 75 microsec for the Intel X-25E) and they will typically support many thousands of IO's per second. It's this 100x advantage over spinning disks that really makes SSD's extremely fast.
However SSD's are not all roses, unlike spinning disks they have dramatically different read and write performance characteristics and performance changes significantly depending on how full the drives are rather than where the data is. Operating Systems are still catching up with this and realising the full potential of SSDs can still be quite a challenge. Finally SSD's are in general less reliable than spinning disks despite being solid state devices. If you are considering putting "an" SSD into a server then you really should be using that SSD only for data that you are fully prepared to lose.
Take a look at this site, maybe your exact disk is listed: http://www.reportlabs.com/testbed/version1/hdv1/hdt35in.php
Todays (at least I think) fastest SATA drive is the Western Digital Velociraptor with around 100 MB/s read/write.
Edit: Don't take the SSD read/write speeds for granted. Mostly these are synthetical benchmarks and mostly they're comparing sequential read/write which is not the only criteria that matters (look for 4K random read/writes, too).
