sizzling :
There no benchmarks yet and I have not heard of any 4gb versions. You need to wait until early next month before anyone can answer this with any facts
There is definitey a 4gb thats the $200 version thats been talked about, the 8gb is $229. Not sure where the OP gets that there will be a reference 8gb vs a partner 4gb, everything indicates there likely will be reference versions of both and since we have seen nothing from the partners at all yet its possible the first month its out it will be all reference style.
As for benchmarks so far the ones that are out put it ahead of an R9 390x, but they are manufacturer released, and while it uses WAY less electricity (150w) than prior cards, thats about the extent of info we have on efficiency.
Until they end up in reviewers hands everything is speculation or manufacturer numbers which can be half-truths..