I am biased, being the CTO at Marmalade... but if your key requirements are (1) camera access and (2) the ability to "squeeze out every little bit of processing power available" then Marmalade is a great choice.
Marmalade compiles your C/C++ to native ARM (or x86) instructions... no transcoding, no virtual machines. It's very easy to bring across existing C/C++ code, nearly all the C/C++ standard libraries are supported, etc. And you can use ASM code within your project. Also, you can do all your development either on Windows or Mac, regardless of what platforms you deploy to (yes, you can even compile/test/deploy to iOS purely on Windws).
