Why on earth would you be worried about your Gpu usage being 50% when playing a game.
If it gives you a decent frame rate in the game with most of the graphics options turned on at a good resolution you should smile.
If it was at 89% it would mean the game was maxing out the capability of the card.
Push the settings up in the graphics options, and resolution and it will rise.
How bad a card performs, is down to screen resolution the game is played at.
How high the Anti alias is set to,and And the texture resolution settings.
Motion blur. ect. ect.
Most games auto detect the best settings for a card as to not max it out.
To give a decent frame rate while playing.
Done by lowering or turning down effects or options of the game.
The load on the Gpu is reduced.