I almost feel like packing the first word with vowels isn't even particularly helpful. I've kept with the same two starting words -- slate and round -- and it has been very easy to guess by the third turn every day. In fact, the only day it took more (5) is when I strayed from using round as the second word. If nothing from those two words hits, the remaining letters leave only very obvious words using I and/or Y.

There really aren't that many 5-letter words, so there's going to be a few specific combinations of two starting words that rapidly whittle the list.