As far as I know 750M is much faster than 6770M. Did you try the patch and suggestions (hiding the Launcher, changing scalability settings) from here: UE4 Perf Woes - iMac - Platform & Builds - Unreal Engine Forums?
As far as I know 750M is much faster than 6770M. Did you try the patch and suggestions (hiding the Launcher, changing scalability settings) from here: UE4 Perf Woes - iMac - Platform & Builds - Unreal Engine Forums?