I too have an older i7 920 cpu and my board also is limited to 3gb/s sata, but when I got a new ssd drive I also got one of these:
Would be great if there was a similar inexpensive way to upgrade SATA 2 notebook MB's, though all of my SSD's are SATA 3, can't take advantage of the full potential offered. But still get a 7.7 WEI score (for SSD) on a 128GB Crucial M4, on the Windows 7 Pro install of my Toshiba notebook built in 2010 (Satellite A665-S6086). Also have a 2011 MSI notebook (FX603-064US) that performs similar, though CPU/RAM scores are higher to reflect the installed i5 (same frequencies as the OP's). 2.66 with 2.93 Turbo Boost.
Though the OP's CPU is dated, there are many who would covet the opportunity to grab the computer as a whole (being the 1st owner gives a huge boost), would make an excellent home server/spare computer, possible Media Center PC, gamer PC (with the SATA 3 controller above) or a 24/7 dedicated number cruncher for a project such as folding@home.
This PC still has unleashed potential & years of life left in it.
Here is a brand new upgrade CPU from what you have, but cost is a factor here. That would purchase many later models, but on the other hand, shows it's still in demand.
Further specs per Intel.
I looked all over the place for a new MB (with latest as possible features) to replace what you have, but keep ending up with "out of stock". Even if these were available, would be expensive. I'm sure that eBay are flooded with these, but I wouldn't obtain such critical components there. Maybe a used upgrade CPU for many computers for under $50, many far less than that, but a MB, no. I wouldn't do it, nor would recommend to anyone else. I can swap a CPU normally under 15 minutes, but the MB takes time. Too much to be messing with used/so called refurb ones.
Personally, I feel this kind of cash would be better put to use on a new system. The Intel CPU's of today uses less power, faster than ever & support is plentiful. I have poured cash into older systems not only for myself, but also others, finding one speedier component leads to another & so on. By the time the smoke clears, $200-300 is spent for what may be an overall 10-15% increase of speed & power. I won't fall into that again. However, if someone else wants to spend their cash & pay me to do the work, I'll happily do the best that I can.
For the time being, the card that Joe C has linked looks promising.