From what I hear, over 25 is the far superior choice. I'm not quite there yet but I put myself down as over for that reason. I would say it's pretty sporadic. About 5 weeks ago I was getting ~2 every 3 or so days, now I just got one breaking a 2 week drought streak. Simply have patience.
Anyhow, I don't think I can hold out till 450. I think I'll hit 300 (256 now) and cash in and be DONE with this site.