Pre flashpoint Arthur's best strength feats were between the 120 to 300 tonne range. He has lifted a city block, held up an 11 story building that's foundation was destroyed while it was evacuated, lifted and upturned oil rigs and carried tankers out of the ocean.
He was durable enough to take small arms fire back then plus survive point blank explosions, lightning strikes from weather wizard, powerful energy blasts, and take blows from Wonder Woman that literally punched him through a wall and across a city and he just brushed himself off and got back into it. he's punched and hurt MM, belted Superboy around, taken blows from Lobo and much more.
Saying that he has shown greater feats Nu52 is simply a sight that you haven't read much of him before.
Iron Man vs Aquaman = IM via Flying + Repuslor Ray's
Iron Man vs Aquaman = IM via Flying + Uni Beam
Iron Man vs Aquaman = IM via Flying + Pulse Bolts
Iron Man vs Aquaman = IM via Flying + Magnetic Control
Iron Man vs Aquaman = IM via Flying + Sonics
Iron Man vs Aquaman = IM via Flying + Freeze Beams
Iron Man vs Aquaman = IM via Cloaking and Punching
Iron Man vs Aquaman = IM via Energy Sword
Iron Man vs Aquaman = IM via Flying + Repluslor Ray's + Uni Beams + Pulse Bolts + Magnetic Control + Sonics + Freeze Beams + Punching + and an energy sword.
Iron Man vs Aquaman = Aquaman. By hitting him.
I'm being mostly facetious, as I was asking for a serious answer.