Following on from a recent aquisition and frame size concerns I knocked up these pics. I probably have too much time on my hands. What conversation will this start, dunno. It may be of some interest to other folks with too much time. 
So how important is frame size?
Is it more about the Pedal/Saddle/Bars triangle?
What about the tilt on triangle, bars over front axel too far, saddle over rear axel too far?
So what size frame is right?
Smaller can be adapted, to a certain degree. (Knees hitting headset is too small). Larger to a lesser degree (bad back).
I believe frame sizes are a rough guage at correct bike size, very rough.
19.5" 2009 Felt
My comfiest ride, or the one I'm most used to, or the one that suits my trails?
Felt overlayed with a 16" Zaskar.
Wheelbase is shorter, bars can be pushed further away with a stem, probably without pushing the bars too far forward.
Felt overlayed with 19" Stumpjumper.
Wheelbase is pretty much the same, but bars are lower and further forward.
Felt overlayed with 16" Hahanna rigid.
Wheelbase is the same, bars the same just lower.
Felt overlayed with Trek Flat Bar roadie.
Wheelbase is so much shorter on the roadie.
My Slideshow shows how much bikes vary and yet are all still rideable by the smae rider.

So how important is frame size?
Is it more about the Pedal/Saddle/Bars triangle?
What about the tilt on triangle, bars over front axel too far, saddle over rear axel too far?
So what size frame is right?
Smaller can be adapted, to a certain degree. (Knees hitting headset is too small). Larger to a lesser degree (bad back).
I believe frame sizes are a rough guage at correct bike size, very rough.
19.5" 2009 Felt
My comfiest ride, or the one I'm most used to, or the one that suits my trails?

Felt overlayed with a 16" Zaskar.
Wheelbase is shorter, bars can be pushed further away with a stem, probably without pushing the bars too far forward.

Felt overlayed with 19" Stumpjumper.
Wheelbase is pretty much the same, but bars are lower and further forward.

Felt overlayed with 16" Hahanna rigid.
Wheelbase is the same, bars the same just lower.

Felt overlayed with Trek Flat Bar roadie.
Wheelbase is so much shorter on the roadie.

My Slideshow shows how much bikes vary and yet are all still rideable by the smae rider.