You'd be able to check focus, BUT it would be frustratingly slower. Compared to a Mac Pro with higher bus speed (1.33 GHz vs. 800MHz) and more CPUs and more RAM.
An analogy would be:
Turn on your sink faucet full blast (non-stop captures streaming in). Now, stick you finger every now and then interrupting the flow. Get it?
It happens to be a world of difference, and why people haul heavy Mac Pros on location instead of using a laptop or iMac (which uses laptop motherboard and CPU).