OBS Frame Rates Issues

I am an avid Rainbow Six Siege player who wants to stream his gameplay. Now I understand that as a starting streamer 720p 30fps streaming is the only worth it route to start with however when streaming Rainbow Six Siege I get awful frame rates in the high teens in OBS Studio and I have tried various settings in game and in OBS to try and solve the problem. I have also asked around in various Rainbow Six Siege streams and no one there seems to be able to solve the problem there either. I have even gone as far to buy a streaming PC using NDI outputs to try and reduce the load on my main PC yet the results are far less than satisfactory. Playing the game in borderless windowed solves the 30fps issue but I still can’t go as far as 60fps which is what I would want since streaming a shooter in 30fps isn’t the most pleasant thing to look at and playing in borderless give so me terrible input lag in game which I am not willing to deal with. Please help me solve this, specs of both computers are listed below along with the settings I play with in game. (Should be noted that all issues are on the gaming PC and not on my streaming PC). With the specs listed I have no reason to believe that the computer should not be capable and everyone who I have explained this issue to is also baffled that I cannot stream the game at 720p 60fps when people with lower spec PCs do it on the same settings I play at. I should also note that I am stream with a 4000 Kbps bitrate from my streaming PC and my Gaming PC sends an NDI output set to 50000 Kbps bitrate (changing the bitrate on the NDI has not shown any difference in frame rates)

Gaming PC:
Motherboard: MSI Z370 Gaming Pro Carbon Series
CPU: Intel i7 8700K @4.3GHz
GPU: MSI GTX 1080 Gaming X 8GB
SSD: Samsung 750 EVO 500GB
HDD: 2TB Seagate 7200RPM
RAM: 16GB DDR4 Corsair Vengeance 2133MHz
PSU: EVGA 550W GOLD

Streaming PC:
Motherboard: GIGABYTE Z370P D3
CPU: Intel i3 8100 @3.7GHz
GPU: Palit GT 1030
HDD: Western Digital 500GB 3000RPM
RAM: 8GB DDR4 Patriot 2133MHz
PSU: Corsair 450W Silver

In Game Settings:
Graphics: Minimum except shadows on medium (No anti aliasing as well)
Resolution: 1920x1080
Aspect Ratio: 16:9
V-Sync: Off
Display Mode: Fullscreen