My Android Coinbase app does not list Circle Dollar (USDC), yet. I do not have a Premium account, though.

While Coinbase allows trades directly into USD, USDC may prove to be a better method of transferring value from Coinbase to other exchanges, assuming that the transaction fees and time are less than BTC or LTC. Its stability will limit arbitrage opportunity costs that may occur during the transfer between exchanges. You might use this as the basis for one of your experiments. I'd love to see the time and fee cost of a transfer from Coinbase to Binance (and back again). Keep up the great work.