Siver need lifesteal early?
My general progression is IE-PD-LW-BT Is this viable or should I through in a VS instead of waiting later for when im getting bt?
My general progression is IE-PD-LW-BT Is this viable or should I through in a VS instead of waiting later for when im getting bt?

Split push like your life depends on it.
If anyone tries to come for you, hit R and run like a bitch.
Insta-clear minion waves with W and Q after pickaxe.
If need be, and especially since cinderhulk junglers are on the rise, you can rush Botrk early for sustained fights over PD. It won't give crit chance, but your sustain will be up the butt and your dps (sans crit, of course) will remain relatively the same.
I usually do:
First
Prefer over PD since Sivir lacks burst damage and it gives slightly more movespeed and improves her already fantastic teamfight damage. You can also sit on avarice for a bit since she's so easy to farm with safely.
I never, ever get lifesteal before these two items other than maybe a second dorans blade. The 2 item power spike above is way too good to delay, even by a vamp scepter.
Next two items. I usually get BT before LW unless I am against a team with a lot of armor. (EX - Graves + Taric lane, or top and jungle tank)

Progress your build from there, and make sure to try and get LW by the ≈25-30 min mark, and make that a priority item to get after your AS item.
I prefer
on Sivir, she's just so mana-hungry, and the CDR really pays off.