The GPD Q9 PSV is also a good choice for playing ps1. I never experienced any gliches, latency or lags while playing. I use stock rom and standard epsxe settings, the PSV sticks are just perfect, the 7 inch screen is big enough.
I am currently playing with Crash bandicoot 2, 3, Ridge Racer Type 4, Soul Blade, but no slowdown or any problem.
Last but not least, the Q9 is much cheaper than the XD