Defeated Smough and Ornstein on my 4th try (without summoning). I was gunning for Ornstein's soul (for the DragonSlayer Spear) so it took me a while to get the pattern down to kill Smough first.
It's quite easy once you see it, since Smough blocks most of the attacks (except the Lightning spear throw) of Ornstein, if you position him between you and Ornstein. Hardest part for me was figuring out how to succesfully block the majority of Super-Ornstein attacks and still have enough window of opportunity to strike him. I ended up using one of the broken pillars for added protection and the rest of the fight went quite smoothly.
It helped to don the Havel helm and Gloves for amazing lightning and defensive protection, plus the Ring of Steel Reinforcement, and using the Eagle Shield. My weapon was the Lightning Spear + 5 for Smough and the BK Halberd +4 for Ornstein (which only did 120 damage, even at 436 att).
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"
