Totally understood, profitability is the biggest concern obviously since I dont know how long this sweet deal will last. I can trade the currencies myself on the exchange. I guessa better question would be, why switch to Ethereum if you could generate more Zcash coins with your new rig? Just for the risk of zcash dropping off?
I am mining ZCash on my old 280X rigs because they are only 3GB cards which isn't really enough to mine Ethereum (put 12 280x cards into whattomine.com), but newer cards have more memory etc. and can mine ethereum more effectively.
Currently, I am keeping my ZCash, but when I get new rigs I will mine Ethereum as I personally believe Ethereum has a brighter future than ZCash. (But that is my own opinion)
Also, as highlighted above, once you get your mining rig working and not crashing, LEAVE IT ALONE! I can't tell you how many times I have tried to tweak my rigs chasing that extra MH/s, only to have it start crashing again (even when I change the settings back to what they were before), which costs more than the profits of the extra hashes. Rigs can be temperamental things...