Iron Counterweight

Barberous Blade:
138-207 dmg
3.20 speed
53.9 dps

With 3% counterweight:
138-207 dmg
3.20 / 3% or 3.2/1.03 or 3.1 speed
55.6 dps

With +7 Enchant:
138(+7) - 207(+7) or 145-214
3.20 speed
56.1 dps

With +9 Enchant:
138(+9) - 207(+9) or 147-216 dmg
3.20 speed
56.7dps

With Fiery Enchant:
(assume a 10% proc rate; unfavorable)
53.9dps = 3234 dmg per minute
3.20 speed = 18.75 swings per minute
10% of total swings minute = 1.875 swings proc in that minute
1.875 * 40 = 75 dmg from procs
total dmg = 3309
55.15 dps

With Fiery Enchant:
(assume a 20% proc rate; closer to what people report)
53.9dps = 3234 dmg per minute
3.20 speed = 18.75 swings per minute
20% of total swings minute = 3.75 swings proc in that minute
3.75 * 40 = 150 dmg from procs
total dmg = 3384
56.4 dps

(yes, Enchant procs are a set proc chance, not variable by speed, making them much more ffective on fast weapons...I included the popular Fiery though for comparison purposes)

As of 2.2:
20 haste rating (for a lvl 70) is ~1.3% increased attack speed.

While power leveling BS, this is a very useful plan that will save you time and gold skipping the large amount of iron you would need making the green scale stuff from 165-200. This is somewhat trivial based on your server prices for mats but iron was very scarce when I undertook PL'ing BS.