PS3 app and high bitrate content

I have a gigabit network and store mostly mkv remux copies (aka same bitrate as the blu-ray) of my discs for use with Plex. Plex works beautifully on my PS4, but on the PS3, it will pause roughly every 5 seconds to buffer. It works fine for lower bitrate material, but the higher the bitrate, the worse it gets. Both PS3 and PS4 are connected via Ethernet cable. I changed the H.264 level to 4.1 also, which didn’t change anything (I didn’t think it did). I simply assumed that seeing as the PS3 can play a blu-ray, it could play a blu-ray rip.

I did some digging and saw the posts from Plex staff regarding the state of the PS3 app. It mainly address the app being sluggish, but there were a few things I wanted to clarify: As it stands, is there no way for me to stream my movies in their original quality to the PS3? I am not interested in transcoding as it defeats the purpose of storing high bitrate content, as well as my server isn’t high spec to transcode anyway.

Secondly, I read somewhere that the PS3 can only stream 720p, and not 1080p. Is that correct?
If I can’t solve this I might have to look at selling the PS3 and investing in a second PS4 or other hardware.