About FE cooling solution:
If you have a tight miniITX or microATX case, the FE is the better option.
If you have a case with good airflow, the custom versions are better by far.
FE fan does not cool the GPU as good as the custom versions but the custom versions, if you have big issues with airflow in your case, will cause the temperature inside your case to be higher compared if you use FE.
In general, since most people have good airflow inside their cases, the custom versions are simply better.
Regarding performance,
The non-FE version tend to have better power connection solution and as mentioned aboe also have better cooling from the GPU point of view. Thus...you should be able to OC the custom 1070 higher than the FE version.