I don't know why people still giving out somewhat-false information about "2nd GPU will make things go slower." I've seen a Youtuber using older Quadro as dedicated NVENC recording GPU.
Even with NVENC, single-GPU setup will take a hit in overall performance, because frames has to be processed for streaming/recording. If your PC (CPU and RAM bandwidth) is fast enough to handle two video cards doing separate things, dividing workload into 2 GPUs should work fine. I know a streamer who even added a capture card in a single-PC to minimize impact on his gaming GPU, as he wanted to play games in High settings. His YouTube video proves this workaround.
My real question would be; which video card is small but powerful enough to deliver good NVENC recording performance @ 1440p.