the Fs tend to be fast, I suspect because they're designed to work with the very early SAFOX bodies, consequently the lenses are designed for auto focus speed almost at all costs.

Cool! I once shot a friend's brother playing Rugby at Twickenham in the BUSA inter-University final. I wasn't using my 80-320 that day but my Tamron 300 f/2.8 instead, so I can't comment on the AF speed but the 300mm was more than enough range and in fact I'd probably have been better off with the ability to zoom out. In short I reckon you're looking at the right range.

TBH I doubt you'll be disapointed with the 55-300, and in any case I think you'll struggle to do better without spending quite a lot more money.

if we're talking about the kind of football where you're right on the touchline, is your 70-210 really not long enough? Its a good enough lens to take some cropping and the AF is lightning on those (or as close to as Pentax AF ever gets anyway!).

Personally if shooting a football match from fairly close range I would have no problem using my 80-320 or Dad's 55-300, the AF hunts a bit from time to time on both but in good light with a subject which mostly fills the frame I wouldn't expect much of a problem. The problems start with birds in flight and fast aircraft, too small and quick for the AF to lock onto.

I've shot Ultimate Frisbee a couple of times with the 80-320 on my K10D with no real trouble focusing wise.

First, must have no fungus, I wont have a lens in my house that has fungus, it's not worth the risk of it spreading to my other lenses.

Then, must be optically and mechanically perfect. Very minor flaws might be accomodated here if there is an appropriate (large) price reduction.

Cosmetics are nice because they imply a lens has been well cared for, but I'll cheerfully take a lens that's functionally perfect but a bit worn looking if it knocks a few quid off the price. Signs of serious abuse would put me off.

Box, paperwork etc don't matter to me if it's a lens I intend to keep. If I think I might sell it on then they're useful because they bump the resale value up a bit.

it's the old story

There are fast lenses, cheap lenses and high quality lenses.

In general, you can have a maximum of two from that list in one lens.

the F 70-210 is sharper and has faster AF than the DA 50-200, but the DA is smaller and has quick shift, a non rotating front element and better contrast.

I'd value them about even, horses for courses.

The FA 80-320 and the DA55-300 are both much weaker in AF terms than the F 70-210. If you need AF in the same league as the F 70-210 you are going to have to look elsewhere.

As others have mentioned, 320 vs 300 is not a difference worth considering, for practical purposes they are the same and the better IQ of the DA lens will more than make up for it.

My Dad has a 10 Million strap, he has had it as long as I can remember.

Depends on the beer, if it's Tactical Nuclear Penguin, one will be more than enough

just in the interest of completeness Carl, where does the 60 fall in your run down of models above?

I had a 50 for a while a few years ago and must admit I found it quite disapointing, ended up replacing it with a z-50p

perhaps the reason for the price near-parity has something to do with the 80-320 being the best Pentax ~100-300 which is film compatible (both in image circle terms and because it has an aperture ring)?

just a guess.