I chose to boost attack speed first in order to use Vayne's silver bolt ability more effectively. then later on building into stronger attack power and a little life steal to hopefully stay alive and have higher dps. divine blade was chosen as my attack speed booster over other things mainly because it has an ability similar to that of silver bolts and my attacks cannot be dodged. i was also debating whether or not to get another infinity edge at the end opposed to the hextech gunblade. i chose hextech over inf edge mainly because Vayne will be attacking enough to get crit hits pretty often at 37% crit chance and a crit hit + life steal = boss heals. but with a further increased crit chance and 20 more attack damage you could beat down the enemy champs faster rendering the life steal almost useless. i think it sort of goes both ways.