8 isn't really all that challenging. You can pretty much break the game even before you get to the Dollet mission if you play Triple Triad enough to gain access to the best items in the game.
If you play it normally, I can't find any particular stage of the game that was actually challenging, outside the Omega Weapon battle in Ultimecia. Even Deep Sea Research Center and Island Close to Hell/Heaven were pretty easy, since enemies level up as you do.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
