First, "use developer unitinfo" gives you more details when something crashes rather than just "an error has occurred" but you will lose eshop access until you turn that option back off. The splash screen option is only relevant if you have a no screen-init build of a9hl, it lets you use a custom splash screen. If you are not using a9lh or just followed Plailect's guide then it won't make a difference.
As you may or may not know, the New 3DS has a faster CPU, however when running games not designed to take advantage of it the New 3DS will reduce (underclock) the processor speed to that of an original 3ds. The New 3DS CPU option lets you force older games to run at full New 3DS speed which can reduce lag/frame drops in some games such as Pokemon.