how much cheaper does the f8500 need to be for you? if you just need a couple hundred off, go for that. if you plan on waiting for it to be 1000bux cheaper, that may never happen.
still, as of right now, it appears the f8500 is the last 'great' tv you'll be able to buy until oled, or some unforeseen FALD unit, both of which will likely cost even more money for many years to come. if you view the f8500 has a minimum 5yr investment, paying an extra 200bux a year to get the f8500 over the f5300 seems reasonable. I don't know what current prices are like in your market, so excuse me if I'm off on that.
personally, I've underbought before, and it's no fun wishing your tv would die so you had an excuse to buy a new one. this time around, I knew I had to buy one of the top models, and now I'm certain i'll enjoy this tv until it does eventually die, and hopefully by then oled will be mainstream.
so, f8500 is first choice. 64" f5300 is 2nd choice, and I'd say the 60" f5300 should be a last resort really. the extra size, and non-pentile display of the 64 makes it such a better value in the long run. again, you don't want to be looking at your brothers brand new 70" TV's in 2yrs wishing you had gone for the 64" when you had the chance.