This is not about whether or not to fly F, it's whether to pay cash now, or hope for saver F to open up (and risk the F price going up). I'm just saying that I would postpone the decision until the F price is likely to rise. Of course there is some gamble there because the price might go up before you expect. The assumption is that if the price rises, you pay the higher fare (not fly economy). So you are betting money, not comfort.

Although, isn't SEA-ANC in F often under $500? Seems like a poor use of 25k miles. Save 25k miles, pay cash, earn RDM and EQM (incl. CoS bonus) on top of the 25k and you're half way to your next CX business class award. It's worth considering, at least...