I always use cpu max speed. And I recommend OC even without any mods, specially gpu. Since the game uses dynamic resolution, OC means the drops in resolution will be less severe.
I tried to change sharpen settings and remove dynamic resolution. Don't know how things are working but there is an image quality improvement.
Original (portable):
Modified (portable):
If I remember correctly 3ds version was 240p. It's sad that Xenoblade games are poorly optimized. Switch gpu is extremely capable and a lot more powerful than Xbox 360 gpu. We shouldn't see games with PS1 resolution.