Waiting will give you more opportunities to win the good Dwarven Runes - I held 12 provinces at 7/8 during Fairy so I could have a shot at Fairy Runes.
Tournaments may help!
Also, you can win Runes by contributing to other Wonders, even before you finish the Research. So, it pays to keep an eye on other cities and pick up any runes that may be going at a bargain - or just be one you really need.