Increased Attack Speed

The idea surrounding IAS is simple: the faster you attack, the faster you apply damage. The more damage you do and the faster you hit, the faster stuff dies. A bow with heavy damage may be passed up for a faster bow with a less damage, since the principle was that it was far better to cause a medium amount of damage with an insane rate of fire than it was to cause a lot of damage with a standard rate of fire. Higher amounts of IAS mean that heavy-hitting elemental skills like Freezing Arrow can be fired faster. High IAS also means that non-elemental damage effects are spread even faster; while the first volley of arrows might not take targets down, they can get slowed, knocked back, stunned, crushed or cursed right away and with a high-speed rig, they'll stay that way.

Proponents of IAS have elevated IAS into an art form that takes up too much space and uses too much math to be used by this guide. The following list of IAS breakpoints comes courtesy of brianc84's Revised Strafe Breakpoints in 1.10.

First, IAS values for bows, starting with the slowest bows first. To reach a "breakpoint," you'll need the minimum amount of IAS needed to reach that attack speed. Any excess points into IAS are lost unless they reach the very next breakpoint.

When you see a notation like "9/2" or "11/3," this refers to the bowazon's strafe cycle. (See Strafe for more information.) The first number is how many frames it takes for the bowazon go from her ready position to the initial attack animation with every bow skill — it's important to strafe because that's how many frames of animation it takes for her to fire the first arrow in a strafe cycle. The second number is how many frames it takes for every subsequent arrow in a strafe cycle to be fired. A bowazon with a 10/3 attack speed needs ten frames to use any bow skill, and when she strafes, she fires the first arrow at this speed and every arrow afterwards until the end of her strafe cycle at three frames.

If you want your bowazon to focus on Strafe, then you'll be wanting to aim for the highest possible speed for whatever weapon you're using. However, if you're focusing on some other attack, then only the first number matters.

Weapon Base Speed [10]: long battle, long siege, crusader bow; long war, gothic, hydra bow; reflex, ceremonial, grand matron bow
Normal Base Frames: 13
Strafe Base Frames: 3

15/4: 0-4%

14/4: 3-10%

13/3: 11-25%

12/3: 26-41%

11/3: 42-45%

10/3: 46-79%

9/3: 80-119%

9/2: 120-156% (Note at there's very little difference between 9/3 and 9/2. Just a FYI.)

8/2: 157%

Weapon Base Speed [5]: short, edge, spider bow
Normal Base Frames: 13
Strafe Base Frames: 3

14/4: 0-5%

13/3: 6-18%

12/3: 18-33%

11/3: 34-36%

10/3: 37-67%

9/3: 68-101%

9/2: 102-131%

8/2: 132%

Weapon Base Speed [0]: long, cedar, shadow bow; short battle, short siege, diamond bow; short war, rune, ward bow; stag, ashwood bow
Normal Base Frames: 13
Strafe Base Frames: 3

13/3: 0-8%

12/3: 13-25%

11/3: 26-28%

10/3: 29-55%

9/3: 56-85%

9/2: 86-112%

8/2: 113%

Weapon Base Speed [-10]: hunter's, razor, blade bow; composite, double, great bow; matriarchal bow
Normal Base Frames: 13
Strafe Base Frames: 3

12/3: 0-7%

12/3: 2-12%

11/3: 13-14%

10/3: 15-36%

9/3: 37-59%

9/2: 60-79%

8/2: 80%

Here're the IAS values for crossbows, starting with the slowest crossbows:

Weapon Base Speed [10]: heavy crossbow, ballista, colossus crossbow
Normal Base Frames: 19
Strafe Base Frames: 5

22/6: 0-1%

21/6: 2-5%

20/6: 6-10%

19/5: 11-21%

18/5: 22-28%

17/5: 29-31%

16/5: 32-41%

16/4.5: 42-47%

15.5/4.5: 48-49%

15/4: 50-69%

14/4: 70-104%

14-13/4: 105-119%

12/3.5: 120-173%

11.5/3.5: 174-214%

11/3: 215%

Weapon Base Speed [0]: crossbow, siege crossbow, gorgon crossbow
Normal Base Frames: 19
Strafe Base Frames: 5

19/5: 0-6%

18/5: 7-14%

17/5: 15-17%

16/5: 18-25%

16/4.5: 26-29%

15/5-4.5: 30-31%

15/4: 31-47%

14/4: 48-74%

14-13/4: 75-85%

12/3.5: 86-124%

11/5-3.5: 125-151%

11/3: 152%

Weapon Base Speed [-10]: light crossbow, arbalest, pellet bow
Normal Base Frames: 19
Strafe Base Frames: 5

18/5: 0-2%

18/5: 3%

17/5: 4-5%

16/5: 6-12%

16/4.5: 13-15%

15/5-4.5: 16-17%

15/4: 18-29%

14.4: 30-51%

13/4: 52-59%

12/3.5: 60-88%

11.5-3.5: 89-108%

11/3: 109%

Weapon Base Speed [-40]: repeating crossbow
Normal Base Frames: 19
Strafe Base Frames: 5

14/4: 0-3%

14/4: 4-6%

13/4: 7-10%

12/3.5: 11-25%

11.5/3.5: 26-34%

11/3: 35%

Weapon Base Speed [-60]: chu-ko-nu, demon crossbow
Normal Base Frames: 19
Strafe Base Frames: 5

12/3.5: 0-7%

11/3: 8%

Where can I get extra IAS?

Equipment:

Rare gloves, bows: +10-20% IAS.

Cat's Eye amulet: +20% IAS.

Goldwrap heavy belt: +10% IAS.

Highlord's Wrath amulet: +20% IAS.

Nosferatu's Coil vampirefang belt: +10% IAS.

Twitchtroe studded leather: +20% IAS.

Various unique, set, and rune word weapons give varying amounts of IAS.

Sockets:

Magical jewels of fervor: +15% IAS.

Shael rune: +20% IAS when placed into a weapon.

Auras:

Fanaticism: starting at +14% IAS.

As far as I know, IAS from Fanaticism is the same as IAS from any other source. Unlike the druid, there are no fancy calculations to make here, just add it all up.