Yes IAS affects strafe. As for the bow upgrade I wouldn't really upgrade any of those. The added reqs for STR would end up losing you damage in the end (points wasted in str could have gone into dex for more damage and higher attack rating). If you are going to upgrade a bow that is in the same caliber as these you should really look into a Witchwild String. WWS kicks ass. Don't get mislead by the stated avg damage. When you factor in Deadly strike per clvl, Chance to cast Amp Damage (actually good chance to cast because % to cast is per arrow), and the options you have with the 2 sockets (I suggest Shael Nef)

Here are the stats:
Two-Hand Damage: (32-35) To (75-81) (53.5-58 Avg)
Required Level: 39
Required Strength: 65
Required Dexterity: 80
Base Weapon Speed: [0]
+150-170% Enhanced Damage (varies)
Fires Magic Arrows [Level 20]
2% Chance To Cast Level 5 Amplify Damage On Striking
+ (1 Per Character Level) 1-99 % Deadly Strike (Based On Character Level)
All Resistances +40
Sockets (2)
(Only Spawns In Patch 1.10 or later)

Every single mod on the bow is very useful for any bowzon. In my opinion the only bow that beat this are WF and a BOTD crusader.