enc28j60 is 5 V tolerant. it doesn't need logic level conversion. the 5 V AVRs read 3.3 V as HIGH. so only logic level conversion needed is for SD card SCK and MOSI.
the 5 V powering is because 3.3 V pin on many 5 V arduinos can't supply enough current.
for new projects use my EthernetENC library (I maintain the UIPEthernet too)