cleanjamie- I will try to give you a short answer...first of all welcome.
1. There is no camera out there that is bees' knees yet or we would all have it
- therefore the choice of your camera depends on your needs.
2. I shoot regularly with all the high end Canikons but for my private use prefer the Sony cameras. Why?
(a) I just love the lenses - there are quite a few Canikon users out there who have now changed to Sony for the fantastic lenses
(b) I love the simplicity of the Sony menu system and literally hate Canon's cameras for that. Each time I use one I have to dig deep into the menu system to change something very simple...drives me bananas!
(c) the reproduction of colours is outstanding with the Sony cameras
...and many more things
2. You bought a high end professional camera that needs to be used in RAW and the files need to be tweaked- something that is the case with nearly all high end models! I am not sure how good you are at post-processing but you need to develop the files "correctly" in the RAW processor (I use Photoshop ACR- it works best for me- and I had to test pretty much all raw converters out there- don't touch Sony's own- it is crap!)
3. If you are into high ISO shooting - which means literally sports or regular low light shots than Sony is not the right choice for you- go for Nikon instead. If you are into anything else- studio/ fine art/ landscape/ fashion/ birds...Sony is the right choice.
4. Sony cameras CAN deal with high ISO very well you just need to be careful with post-processing. But than I always ask myself- when is it the case that you need to shoot at ISO6400 (btw they have tested Sony's ISO vs Nikons and it turned out that Sony's ISO6400 is about as light sensitive as Nikon @ ISO12800!)
Here are some high ISO shots with the Sony A900:
As said you need to learn a certain workflow with the A900 but than that's the case with every other camera out there. I assume you shoot in RAW?
Hope this helps? Any more questions please shoot- I could go on and on about the advantages of Sony over its competitors but than somebody else would do the same about the Canikons...