I highly recommend you amend the header to read:
"Saffire Pro 40 vs Presonus Firestudio"

Yes, I know it's a little more expensive than the Project, but the input/output options and routing are more than worth it, IMHO.
W/ the Project, you can only daisy-chain another Project or a Tube. W/ the FS, you can ADAT virtually ANYTHING. (up to 16 addt'l channels @ 44.1k, 8 @ 88.2k). Plus the Control Console and optional MSR are really nice to have. Really nice.
The customer service has been great the few times I've had to call. Always someone readily available (normal hours), always w/ enough knowledge to walk me through anything.

I can't comment on the Saffire other than to say the guy who has "mentored" me got the 26 model over the FS a few years ago. Plus, I would guess that the preamps in the Saffire are a little better. Focusrite makes some nice preamps, but not sure that holds true for their cheaper stuff. Anyone?
The FS still has more I/O capabilities though.
One major disadvantage to the FS is that you can only enable phantom power on channels 1-4 and 5-8. No individ'l switches. Also, I'm not sure it has true bypass of the preamps.

I know I'm coming awfully close to schilling for this product on these forums. However, it has been my one and only interface for about 2 years now. Getting the drivers and firewire straight was a little annoying, but since it has served me wonderfully. I can't say enough about the I/O. You can do anything routing-wise w/ this thing w/ some creativity.

For example:
I've done some events at the studio (church) where I have 3-5 soloist/bands perform. I record it all (as much as 16 channels), can listen on 2 sets of monitors, a sub, and headphones, send a feed to PA for front of house, and still have another ST out (2 mono).
B/c of the console and it's routing, each ST mix is discrete, so what I hear in the CR can be different than what's heard in FOH. You can even route a pre-recorded track or mix out to monitor, use in a live performance, or whatever.
I could be doing a lot more still, if the need was there.

There, advertisement over. I appreciate it when someone w/ a good amount of experience w/ a product shares their experiences, and wanted to hopefully return the favor. As always, YMMV.

I can't offer as good of advice as soapfloats, but I have the Saffire PRO 24 right now and I enjoy it. I was looking at the firebox and this one because I don't need much out of an interface and what set the saffire apart for me was the reviews. I have always hear that Presonus has good preamps which is something that made me want to try it out, but then I heard they fall apart easily and lose their signal often. The saffire had only good reviews so I tried it out and for the past year it has done a good job for me. The only issues I have with with it are sometimes it is a little quiet so I really need to crank the levels to get the sound I want, and it causes a weird buzzing noise through my rokit g6 monitors. I think that could also be caused by other reasons but I still here it. I hope this helps a bit.