Ok. Here is what I think of the Satio if I have to compare it to the 5800 which I'm still trying to sell. lol
Positive points imo
HSDPA speeds are excellent. Online browsing using Skyfire browser is awesome. I haven't used it as a modem yet connected to my PC at home, which I did a lot with the 5800, but I'm sure that will be the same, if not better than using my 4mb ADSL at my studio.
Overall Speed of the phone. Well, you just can't compare. Opening apps, playing games, etc... is so quick. Especially 3D games like "Let's Golf" and "Ferrari 3D".
Camera as we all know if much better. Not only still pictures but movie quality too.
GPS is also very quick. You get a lock in about 5 seconds, something that was only reachable on the 5800 after a few software updates.
The overall feel of the phone is also very solid. Some people say that it scratches very easily, mine is still fine.
Call quality is on par with the 5800 which imo is very good. I don't think you get better call quality on any phone other than a Nokia.
Negative points imo
The battery only lasts 2 days if you play with it a little bit. With heavy usage you should have to charge it every night while you are sleeping otherwise it will go dead during the next day. I switch mine off at night.
Overall I like the Satio more than the 5800.