We are not in bull market so how it you are expecting 800 dollar from ethereum, it is 125-130 dollar now and it must do x5-6 in few weeks:) I think we must put reasonable target if we are writing it at somewhere.
Basically you shall try to create an analyzation about how much the block reward will have decreased, after you will see how much being reduced and then you can try to take a reasonable speculation about the ethereum market.