Caching those tables into SGA (buffer pool) would help only if you accsess those tables exclusively with full table scans. I doubt this is is the case.

If those tables are accesed via indexes (most likely), then you should cache all those indexes too (I doubt that this is feasible if there are couple of indexes on each of those tables). And if this is true I doubt that *all* rows of those tables will be accessed very frequently - usualy some rows are visited far more often than the others. In this case I would simply supply enough buffer cache and let oracle fill it up with those table's blocks eventually.

But I'm wondering what makes you belive you realy nead to cache all those table in whole. Have you checked what is your buffer get hit ratio? Can you let us know this % and the natuer of your database (data warehouse, erp, transactional,...)