In case of DXSTUDIO the bad performance were not due to the lacking of a scene management system since I used animated models only Anyway the difference was impressive, not just 2-3 fps, I mean
I wonder whether new engines are not optimized for old hardware
An other potential problem I use Fragmotion and MilkShape same as many others hobbyiest programmers ,I suppose Unity support none of the file formats exported by the low priced animators I dont like Blender I should use a converter but I have alwayes had a lot of problems with converters particulary with complex file formats such as FBX
