It does not matter what software you are using - they all use same 3rd party codecs to encode the video.
Huffyuv/lagarith - lossless codecs (huge file size), very little cpu usage.
Mjpeg/RTV1 - lossy, high file size codecs, light cpu usage.
x264 - lossy, smallest file, huge cpu usage.
H264 (hardware) - no cpu usage, uses videocard to encode the video (intel/amd/nvidia), small file size. Shadowplay uses H264.
If you have enough disk space (considering 1 minute = 1 gb) - try saving and huffyuv/lagarith or MJPEG/RTV1 and encoding later.
If you do not have enough space - you can try utilizing H264 codec that requires OpenCL (i think your amd hardware should have opencl enabled). I think OBS should have this codec available, and msi afterburner should have it available too in some future.
Also, try reducing game fps to 30 and resolution to 720p - those are specs youtube converts video to anyway, so playing/recording at higher is pointless.