Buying 4GB GPUs -Makes sense?

Hi everyone. I am looking to create my first rig for mining RVN. And I can see there is a reasonable (still way overpriced but thats the current market) supply of older 4GB cards out there that are no longer used for mining ETH. I do understand 4GB is enough to mine RVN however would 8GB help with the better hashrate? Also would 4GB in a year or so be also too small for mining RVN? Thanks!