Should I wait for a sale?

I know that Riot tends to do a sale on rune pages at some point and I currently have enough to buy a couple if they go on sale soon. But my question is: Is the sale close enough for me to hold onto my IP for it and just keep grinding so I can, hopefully, get four instead of two, or is it far off enough for me to have enough time to grind my IP back up? If I have the time then I could just grind my IP back up for the pages and then focus on filling them out later.

So, what say you, members of the board?