crap period to war(if you didn't finish the rush by that time, you probably didn't rush in the 1st place), the tech opening them has nil trade value on high lvls. so I research it once in a blue moon(trading for it when backfilling), if you waited for iw, you'll also have to wait for construction since probably you'll have 20-40% cities, eventually with whipped walls if the chap is protective(another nono tech, since the ai also prioritizes this - again - higher lvls., no clue on monarch and below, but even on emperor construction used to come too late unless I had jumbos nearby), longbows will always come up earlier then you'd like and close the window.
all in all, on paper it's good; in practice, I avoid warring at that time like a plague. Good for taking the barb. cities and unlock the he and that's about the only more or less constant use I've found. Axe rush or postpone to medieval.