New Bike - Is Carbon a must?

Not a must.  A good aluminum frame is still a good frame.  There will be a bunch of differing opinions on which is better and why, but the answer to your question is no, carbon is not a must. 

Proper fit and well operating components are a must.

Not a must but more of a personal preference. If you're "looking for perfomance gains based mostly on getting a proper fit" then frame material is nearly irrelevant.

Just want to note that Cervelo makes the P2SL which is essentially the P2C in aluminum.

Ride 'em both, ride 'em all and decide for yourself.

I'm am not a fan of Carbon bikes - they can flex and I am 220 lbs and do not like the feel of the flexing - also - like many materials Carbon does have a life - it is shorter than Alum and other metals,  so I look at the bike as a long term relations.

Lets see:

I own a carbon frame
My wife owns an aluminum frame

My wife has beat me at every race we've done together...

Point being, at the end of the day it's about the rider. 

Yes it will.  Design parameters allow much broader range of frame and tubing shapes.  That is why the fastest mass market frames (in terms of wind tunnels and race results) are all carbon.

Not always.  A good builder can build any material in a way to accent one or another feature in a frame.  I've ridden carbon that will rattle your teeth out on the bumpy stuff.

Because it's generally a myth.

And how did you come upon believing that this was a myth?  Are you just believing what others say?  I'm an enginner and i deal with materials on a daily basis.  Not to say that i know everything, but from my experience i and background i believe that this "myth" has merrit.  Anyway i don't want to hyjack this thread so i'm leaving it at that. 

Carbon may be faster due to the aerodynamics, but everyone is right when they say it come down to the persons fitness.

From engineers who build bikes. 

The material itself may have certain properties in isolation, but it's how the bike is constructed that makes the most difference.  And on that score, as I think Daremo and some others noted above, a carbon bike can be made to be more "stiff" or "harsh" than alumium or vice versa.  Things like fit, saddles, tires and air pressure are all likely to have a bigger impact on road vibrations than carbon vs. alumium (or other material).  Perhaps an "everything else equal" bike would ride better in carbon vs. aluminum but I think you'd be hard pressed to identify that bike.

So it sounds like he is agreeing with me.  "everything equal" which it would be...A carbon bikes would ride better.  Of course if the carbon bike doesn't fit you as well as the aluminum then thats obvious which one is better "for you".