Things are a bit less linear when you take haste into account :
A 60/20 1-hander can be lowered to 60/10 with 100% total haste (delay hard cap used to be 10, but i read somewhere that it's 9 now... any info on that ?) which turns into a dmg/dly ratio of 6. At 70 with all AAs, dual wield/double attack checks are pretty much in the 90-95% range so dual wielding 60/20s yields a total dmg/dly ratio of about 12.
A 180/40 2-hander with capped haste (133 or 135%, not sure here) turns into a delay of 40/(1+1,35)=~17 which yields a ~10,6 dmg/dly ratio
(Note here : some time ago i've parsed a long practice dummy bashing to see how triple attacks does affect 2-handers dps... result was that you can pretty much count like if you had a 100% double attack rate, but not much more)
If you want to compare weaps, don't use anything above 24 delay since from that point on, it's not possible to bring the weapon to the delay hard cap.
Add in procs and dual wielders >> 2-handers dps-wise, with the situational high-DShield-bosses where 2-handers usually shine.... a bit
Damage wise : using <24 delay 2-handers and putting a focus effect on them to offset the difference in number of procs may work, but it'll require quite some fine-tuning.
2-handers should proc approx 2x as hard as 1-handers, so if the 1-hander has a +50% dmg focus (i.e 2x150% proc dmg), the 2-hander should have a +200% dmg focus (1x300% proc dmg.
(NB : don't forget SKs already have +300% dmg on their lifetap procs via AAs)