A few days ago i changed string gauges from DR 10-52 to DR healeys 10-56 (i keep my axe in drop c). I set the floyd up so that it was level. 2 things happened:

I noticed that the 4th string (C) would buzz a lot more than it used to. It only buzzes when i fret the notes (no open string buzz). I tried the following:
Raising action by raising the bridge (OFR) --> helped, but i had to get it much higher than i like it in order for the buzz to disappear.
Then i adjusted the truss rod a bit to add more relief (which didn't help).
I have run out of ideas on this one, what could be the issue?

I also noticed that the intonation was out (on the same string only). I have tried to adjust it, but i have to increase the length of the string almost as far as it will go in order to get it properly intonated. Is there anything to worry about here?
The slightly heavier lower end strings would increase tension on the neck so you ended up with slightly more relief to start with before adding more later.
Intonation is always affected by string size and string pull so changing gauge and to some degree tuning affect it directly and indirectly.

Buzzing in the higher registers can be caused by too much relief as you are fretting notes in a depressed area in the middle of the neck.
Moving on.....
So i should decrease relief rather than increase, right?
And about the intonation thing: i was worried that it seemed like a rather large adjustment for a 0.02 string gauge change. I am used to the lenght of the 4th string having to be one of shortest. If i adjust it so that the intonation is correct, it becomes the longest, thats what i find awkward.
I think JJ1565 has a link in her sig for setup advice.
But basically you need to re-access and adjust relief for your new gauge, then adjust height, then go thru the intonation procedure. Personally I don't like the harmonic method and prefer to adjust to open string & fretted 12th fret note as it compensates for the depressed string length. It's also immportant to check and adjust with the guitar in it's playing position (not lying on its back) and to keep your fingers off the tuneing pegs when checking the note as this can affect the pitch.
Moving on.....