Has ANYONE actually set-up various french drain configurations behind clear plexiglass (cut away-like an ant farm display) to see (for real) how it performs?
In my 'minds eye', the possibility of collapse (despite the corrugations (I've seen crunched perforated pipe at the store!)) and the idea of standing water within the corrugations makes the flex pipe less of a candidate behind a retaining wall 4ft or higher in a clay environment.
Solid perforated PVC: Hmmm...Holes up lets water in directly above the pipe and that's it. Holes down hopes water will find a path of least resistance and voluntarily enter the pipe on a journey to a desired outlet away from the retaining wall to alleviate hydrostatic pressure.
It seems best to combine the best attributes of both systems to use solid perforated pipe with holes drilled/punched all around to ENSURE water finds its way inside to travel down stream.
Regarding the water seeping out...yes, water will seep out under low or zero precipitation conditions where water behind a retaining wall will not be an issue. However, during moderate to heavy precipitation, water will be taking the path of least resistance, once it finds its way into the pipe, and since water is draining through the backfill stone everywhere, flow into and through the pipe downstream until precipitation subsides. Keep in mind, appropriate airflow needs to exist for water to flow. Keep the outlet above ground/water level taking into consideration for water pooling at the outlet.
None of this is proven...just my minds eye perspective.