Once ETH goes Proof of Stake fully, ETC will be INFINITELY more profitable to mine than ETH will be.
For that to happen, price of ETC must go 20-30 times up
The price won't matter, once ETH goes fully Proof of Stake income from mining it disappears as there will be NO MINING any more on it.
That's also going to dump profitability on ALL GPU mineable coins across the board though as the (currently) 9 million or more GPUs mining on ETH look for new homes, and will hammer profitability even harder on any remaining ethash coins as the E3 units in use by then look for new homes.