Assuming quiver bonus of 15% and BM bonus of 20%, that's 38% faster attack speed (it's multiplactive, not additive). Let's assume 1700 AP (benchmark in Aethien's guide), 20% crit chance (and crits do 230% damage, so 20% is 26% increase in DPS), and 32 DPS arrows (highest vendor arrows with no rep req). And for the sake of arguement, equal all other stats (except weapon damage and speed - what we're focusing on).
So you get 121.43 DPS from AP, 32 DPS from arrows, and then the speed bonus is factored in.
Weapon 1: 130-242 damage, 66.4 DPS, 2.8 attack speed.
Weapon 2: 204-307 damage, 82.4 DPS, 3.1 attack speed.
Adding 153.4 DPS to a 2.8 attack speed weapon would result in 429.52 damage increase, or 556-672 damage. The 38% increased speed is 2.03 attack speed.
Adding 153.4 DPS to a 3.1 attack speed weapon would result in 475.54 damage increase, or 680-783 damage. The 38% increased speed is 2.25 attack speed.
Steady shot would do weapon damage + 340, and have a cast time of 1.09 seconds.
Weapon 1 shot rotation (assuming steady + auto)
Auto-shot fires at 0.0
Steady shot starts at 0.0 (assuming spamming a macro)
Steady shot fires at 1.09
Next auto-shot starts at 1.53
Auto-shot fires at 2.03
Note that there is 0.44 seconds of dead time in here. Also, the damage from 1 auto shot and one steady shot would average to (614+526)*1.26 = 1436.4 damage before armor. That's 707.59 DPS.
Also, if you fire off a multi shot you will definitely delay the auto-shot cast by at least 0.06 seconds, and if you fire an arcane shot you will delay the start of the next steady shot by 0.56 seconds (which wont hurt the DPS except to add 0.08 seconds to the shot rotation). So basically, firing anything but auto and steady will gimp your shot rotation, but overall could increase DPS slightly (not gonna do the math).
Weapon 2 shot rotation:
Auto-shot fires at 0.0
Steady shot starts at 0.0
Steady shot fires at 1.09
Next auto-shot starts at 1.75
Next auto-shot fires at 2.25
There is 0.66 seconds of down time here. Enough to allow an MM/SV shot rotation to come in without gimping DPS. 1 pair of shots would do an average of (731.5+595.5)*1.26 = 1672 damage, or 743.1 DPS. Compared to 707.59 DPS above (keep in mind the additional 16 DPS probably paid a part in this).
I'm too lazy to go back and do the math assuming same weapon DPS, etc. However, from what I can gather the slower weapon is actually BETTER due to higher steady shot damage (596 vs 526) and the fact you can weave in a heavier shot rotation.
A 2.9 attack speed would be the minimum that would not gimp a shot rotation (assuming you alternate between shots that include an extra shot...i.e. auto-steady-arcane-auto-steady-auto-steady-multi-auto-steady...). However, you would have to be within 0.01-0.02 seconds of error.
We also didn't factor in rapid fire, but I'm guessing the slower weapon would allow the steady shot to clip less auto-shots (and no chance of throwing in another shot).
One last thing to note, imp arcane shot would not help the build, since the shot cycles take about 2.1-2.3 seconds, you would have something in the 4+ and something in the 6+ range (nothing in the 5+ range which is where imp arcane shot would help).