20" & 30" calibration don't match

Hi

I prcoess images through Ligthroom and Photoshop.

I use a 30" and a 20" aluminum cinema diplays, side by side.

The contrast and color never match.

I have used basic calibration,

advanced calibration from system prefs

and x rite i1.

The 20" is always duller,less contrast & lighter.

The real problem with 2 results is you don't know which to trust.

Any thoughts ?

PS

My machine won't upgrade OS as it is not 64 bit

thanks

D