My Helios used to be 52T-11to30T and I swap for 53/39T -11to30T as a first evolution and it was more useable on big hill but found that I spent most of my time on 53T -13T&18T. The thing I didn't like was the jumps between gears. so I put a 9 spd 11to25T which gives me plenty of smooth power between 53T-12T&17T. With 56T, you should get very nice power.
39T-21T&25T is good on hills, no need for 28 of 30. With 40T, you don't need a high number of cassette teeth.
I am looking into a 56T for mate with a 44T and it would give me a powertrain similar to semi compact 700c.

So will a 56-40 work, yes, it should thing it is the 16T max gap advised by manufacturers and some pro ride with 18/19T gap. However I would consider changing the cassette too to make the most of the double chainring and get something smoother.
Have a look on XL how the gearinch evolves as with various cassettes and chainring.