I have a lot of bikes and the reason I have any of them is because they are first and foremost, comfortable because if I am comfortable I can ride farther and faster and be a much happier camper.
Running your tires at their maximum pressure isn't always the best idea as too much tire pressure prevents the tire from absorbing shock, can make handling sketchy, and cause increased fatigue. The rated tire pressure is only a suggestion and you need to account for your own weight and riding style when setting pressure. I'm a small guy so running my tires at their max does not make sense... YMMV.
The material a bike is made of doesn't affect the ride as much as the geometry, build quality, and other components, especially the wheels and tires.
A tale of 2 well made bikes, one is new and Al while the other is vintage steel.
My Trek 7500 is an incredibly comfortable and fast ride...it runs on Schwalbe CX Compe cross tires (700:35) that I keep inflated to 65 psi / road and 40 psi / trail. The frame is a ZX series aluminum while the fork is steel, I have Ritchey CX drop bars, and a Bontrager saddle that is a good match for the bike (and my butt) and I would have no reservations about riding a century on this bike.
This bike really depends on it's tires for it's ride qualities as the frame is very stiff and almost identical to the frame on my 6700 HT... I have a set of road tires I can run and at high pressure the ride quality really falls off... but the bike does get much faster.
I also have a 1982 Trek 750 that is a fully lugged and built on Reynolds 531 tubing. It runs 700:26 Kenda slicks which are far narrower than the CX tires on my 7500 and run at a higher but not maxed out pressure (90-95 psi) which would make one think it was a harsher ride than the 7500 CX bike but the frame on this bike is really second to none, absorbs a lot of shock, and it too is incredibly comfortable... and fast.
