Dunno, OpenGL is hardware-close, as such the support/performance depends on the OpenGL ability of your GPU/graphics card/drivers. For me, I think, Wc3 ran faster using it but I do not often change my system. What I experienced though is that some borderline stuff deviates. For example in the LightningData.slk you can set the duration/interval of a lightning bolt and I once typed a 0 in there and that crashed/freezed in one scenario while it was okay in the other.