User blog comment:Andrew.heo1/When to Get a 3rd GP10 Item on a Support?/@comment-5412280-20120815160122

You can also consider buying GP/10 runes (quints and seals) if you find yourself getting all three GP/10 items would hinder your ability to provide support. Also, definitely depends on what support you're up against. If it's Blitz, you definitely need wards galore to expose his brush location.

I would also look at how well you are doing in lane as well. If you are getting the assists, you can either buy the KLP, or simply bypass and buy some other support items like Zeke's or Soul Shroud, depending if they are more so AD carry/caster, or pure AA AD carry.