That would be just crazy.
F5: Is a very tricky paper and although is not as time-pressured as some other exams, it is massively time-consuming when it comes to interpreting questions and deciding on what you are supposed to do. I'd avise you to sit it on its own.
F6: Pretty straightforward but loads of rules to learn. Good to be sat with another paper.
F9: I am attempting this in December 2014. My colleague told me it is best to sit this with maybe F8 or P1 (something a little less numbers-based) as all the formulae to learn should really eb second-nature to you. Also quite time-pressured.
So up to you, but take into account all the time you will be investing in studying 3 papers and the realistic chance of passing them all.... Just a thought.
best of luck though :-)