Kenny,

To your first question, yes, you can mix memory sizes.  

To your second question, 4GB of matching memory will be faster than unmatched memory, but 8GB of unmatched memory will be faster than 4GB of matched memory. At some point you stop getting gains from more memory, but that depends on what you're doing.

Is it ok to mix 2 GB and 4 GB DIMMS in an iMac (mid 2011)?
I am modeling fishery CPUE as a function of a number of a number of covariates using a GAM approach that includes fixed and random effects. 

I understand that there are limitations with regards to predicting random effects (predict function only addresses fixed effects) with gamm4. How does the predict function in the basic gam (mgcv, using bs="re") deal with the random effects? Are they included in predictions? Any thoughts would be much appreciated...
