Antoine, Path Tracing is currently much slower, though in some cases it produces much more realistic results in subtle bounced lighting. I would recommend simply testing it on a low resolution render or a crop area, that's the only real way to know how much slower it would be on your scene.
We have an option for "Exaggerate surface details" in the GI settings that *only* works with the path tracer rendering method and can use Ambient Occlusion to create these details. But keep in mind this is not as accurate as the path tracer alone. Ambient Occlusion in particular only darkens, it does not handle bounced direct light off surfaces. It may be a pleasing visual effect of course, it's just less realistic.
Mhaze, I hadn't seen your update when I sent the support reply. However I can't replicate the issue, Double-sided is what causes the issue and behaves the same in 4.2 vs. 4.3. Are you sure it used to work?
- Oshyan