yes, I just started trying out a few N64 games and noticed the lag. But I'm also not using an official raspberry pi power cord, the power cord that came with my pi was a micro USB to regular USB that plugged into a Power Adapter. But the plug doesn't fit snug into the adapter. So I directly plug my cord into a surge protector with a built in USB port. I'm getting a better power cord in the mail today to try out. Power consumption definitely effected my lag in Dreamcast, N64, and PSP games. But PSX always plays falwlessly. That doesn't make sense. Lol.
And yes I had that Tronkyfan theme before. Tried out alot of them. Superdisplay is one of the best ones for any newbie I believe. It allows you to see individual themed collections artwork and you can view 7 systems at once which is superior to most of the themes I've seen. The Star Wars theme though let's you see 9 systems at once and has run fairly well for me recently and with the new movie out now I just have to keep it.
That applies only to a certain kernel version which I don't remember exactly, but I know for sure that the kernel versions on Raspbian Stretch from the beginning doesn't need it anymore, it "sees" all the available memory. You can easily check that for example with free -m and adding the gpu_mem you have configured to that.