Graphics cards for on the fly H265 encoding questions please?

I am an amateur radio fan and have a modest set up for transmitting and receiving amateur TV digital pictures and videos via the `Es Hail geostationary satellite..

H265 being better quality for a given file size and bandwidth would improve my transmissions which are currently in H264 encoding.

As such I want to build a dedicated Windows PC for this purpose. Inputting a live hdmi HD video stream and outputting it in H265 format. Given the scarcity and price of graphics cards right now I have shown an interest in an EVGA GTX1070 SC2 card, used, an acquaintance is selling. Is it likely up to the job or should I look to spend more on a more modern card?

If I stick with Windows 7 Pro 64 bit which I am comfortable with, am I at a great disadvantage to moving to Windows 10 or 11? What would be the best processor and motherboard for Windows 7 and this rather specialised application, I know most later Intel processors will use some of their capability to encode H265 encoding, does having a graphics card GPU doing that render that part of the CPU's capacity redundant? I am also somewhat aware that very late processors and motherboard socketing may not play well with Windows 7 any longer.

I have a PC running an Intel i7 6700K processor on a Gigabyte H170-D3HP motherboard with 16 Gb RAM, which I am using for something else, can I improve much on that and still use Win 7 64 bit?

Thanks for reading and for any advice you might share.

Is simply converting the h.264 to h.265 before transmission an option or do you want to directly convert and transmit the files that you are receiving without saving the files?

Ridiculous as I will sound, I do not know. I wanted to take live hdmi out of my Sony video camera an have it converted on the fly to H265 which is fed into the transmitter. I can use OBS to read an MP4 video file and let the current main PC processor convert to H264 or 265 but it's really struggling. Thanks for the reply.

I'm trying to understand your setup. Are you receiving via your camera and then transmitting from your camera?

To do the conversion, you're going to need some horsepower and a program/app that will stream and convert at the same time.