if I'll use CPU with large RAM there will be no difference ?
"Theoretically." In practice, there are no Arduino CPUs with that much RAM 
I would look at reduced cost Wiznet-based modules before I looked at ENC28J60 modules, for most applications. For instance, you can get the core Wiznet module (SW compatible, but no "shield format") for about $21: http://www.ewiznet.com/goods_detail.php?goodsIdx=125
(adafruit has an shield adapter, but there goes most of te cost savings.)
And then there is the Seeedstudio version, and the random clones from China...