Can you check your OBS settings? Are you using your GPU for stream encoding or your CPU?
Note that your power supply may not be able to handle 2 graphics card and you may have to upgrade your power supply when adding a second card. Many streamers end up getting a whole second machine to capture and stream when they push for the highest fidelity. Is it worth it? Only you can say.
Depending on your game and stream expectations, it's possible to adjust some game settings or stream settings to minimize the impact without having to add additional equipment. Max quality settings can get crushed in compression to YouTube and Twitch and results in diminishing returns - your mileage may vary, watch your own stream after and make your best judgement call.
Sauce: I stream on Twitch as a hobby and will never break even, not quitting my day job ever.