I'm going to keep my vote neutral for now.

Even so I still think that Sivir gets enough survivability/sustain early game from getting a Doran's Blade (or two; possibly along with one point in the Vampirism mastery) to not have to get Bloodthirster as a first item (although I got to admit that Bloodthirster is looking a lot better now that it got a 33.3333...3% increase to it's life steal from patch 4.12; 15%LS>>20%LS). Since the patch 4.12 changes on the Bloodthirster came around I will have to be conducting some experimenting of my own. However, I'd like to state that so far it's become apparent to me that the standard ad carry build does not appear to be the best (or strongest) way to build Sivir. Right now I actually think that the best way to build Sivir is much like a Hybrid AD Caster & Carry (like Lucian). The reason I believe that is because while Sivir's Ricochet (as of levels 6, 11, and 16; On The Hunt) seems like all the other AS steroids (e.g. Miss Fortune's Impure Shots or Tristana's Rapid Fire), there is an imminence difference. First off, (this is more of a counter argument against what I am saying) the other AS steroids are for a duration (e.g. Rapid Fire is for 7 seconds, whereas, Ricochet is just for 3 autos), so you can only reduce their cooldowns by getting CDR (while Ricochet's CD can be lowered by both AS and CDR, however the AS reduces the CD by a minimal amount - about .1 seconds; from ~1.5 seconds to 1.4 seconds for 3 autos- if you count the AS lost while building for 40% CDR). Lastly (and most importantly), Ricochet gives you an auto attack reset (auto attack resets do not scale off of AS, they only scale off of CDR), so if you want to optimize a higher DPS (not short AS bursts) it would actually be better to get CDR, not AS. Then just think about Sivir's other abilities: Boomerang Blade, Spell Shield, and On The Hunt. There has been so many cases in which I managed to kill (or not kill) my enemy because my Boomerang Blade was off of (or not off of) it's CD, and in most of those cases I managed to get that kill all because I had built up CDR. Spell Shield has absolutely no mana cost, and in fact gives you mana back if used properly. When building CDR one would assume that Sivir would begin to have mana problems. Well, if you do your spell order as Q>E>W instead of the standard Q>W>E that will not be the case. You will be able to use your Spell Shield more frequently granting you plenty of mana back (as well as protection from enemy abilities), while saving your Ricochet mostly for it's auto attack reset and AS steroid during trades. Then with only 48 seconds on your On The Hunt at max rank, you get a lot of roam potential (you can even in some cases spam R in front of your nexus on all 3 minion waves while running back to lane; only when you have vision of the enemy team on the other side of the map of course) as well as a frequent utility (escape or engage) for the whole team. I have a Sivir guide of my own (that includes both a standard build as well as a HADC&C build), and while it would not be against the rules to link my guide (being that it is relevant to our discussion) I would rather leave it up to you to find on your own (assuming that you'd want to of course). Since you are experimenting anyways, you should really give the HADC&C build a try.

Hey, guys! The update that went through on June 20th was actually an accident. I was using it as a template for other guides and didn't mean to update it. That being said, given the changes done to Bloodthirster in Patch 4.12 I wouldn't change the build. Her kit doesn't synergize very well with critical chance early game as her only real steroid is post level 6 when her ricochet is activated. Bloodthirster gives you a lot of survivability, which is very helpful given her low range and lack of escape, and the same amount of AD as IE for 300g cheaper. Regardless of which you chose to build first, Last Whisper would still be your second item to maximize your mid-game damage and this doesn't synergize well with IE at all because you want another critical strike item to compliment its passive.

I'll do some experimenting in the meantime to see if I still agree on this standpoint and update you guys if I do change it.

This build will not work for this patch.

So I did some research and I'm kind of disappointed:
http://www.mobafire.com/profile/filipp-414159/activity

This build needs to be updated for the 4.10 patch.

Quick tip, in your team comps section you have a picture of Sona, but in the text you were talking about Nami:

Good Job, Works perfect!