One thing that may also be worth taking into account (other than what has been mentioned) is where you are likely to be diving? If currents are an issue with you being a new (ish) diver then the size of a 5D in an ikelite with two strobes (you will need unless shallow water) and a port for a full frame camera is a large compared to something like the EM5 that could be managed much easier.
I have an EM1 setup in a Nauticam with two strobes and diving with it makes quite a difference to my air consumption at times and that is considerably smaller than a 5D.
If you are diving abroad also consider how you are getting a large setup there as many airlines have weight and size limits for hand luggage so you would probably end up putting a large setup in with checked baggage.
Hope I have not confused the issue further for you...