Thinking of spending my hard-earned IP on Sivir. Thoughts?

My build is usually Manamune, Bloodthirster, Frozen Mallet, Zhonya's Ring, Madred's Bloodrazor, Infinity Edge, Bloodthirster, Guardian Angel, Boots... unless I'm mid, then I go for an early Warmog's for survivability.

I like to max R first with 1 point in W for the CC, which helps my aggressive playstyle.

I rarely see Sivir played, but when she shows up to my lane I always shit my pants and die. Is she worth the IP?