On a laptop and with the strength of both those GPUs, I don't see any need for more than 2 GB. Read this and I think you'll agree
http://alienbabeltech.com/main/gtx-770-4gb-vs-2gb-tested/3/
BTW, I would suggest having the laptop built to your specifications.... store bought lappies inevitably have compromises and are loaded with bloatware and often malware (google lenovo superfish for one example)