I personally go from my experience of how my 1993 ford escort runs on E10 which is a lot different to e5. I know the car well as I've owned it 16 years. I always put e5 in it, unless E10 is a last resort.
My worry is how E10 degrades the fuel lines due to the extra sulphur. Ultimately increasing the risk of pipe degradation and thus fuel spilling into a hot engine causing a fire.
However I appreciate fuel lines should be checked regularly on older cars anyway.