Wow, thanks for all the responses! I had hoped to check back on this thread earlier, but it was a busy night at work. I'll try to address some of the questions and advice that have been offered.
For
most of the swim meet, I used the DA*300, on a monopod. Of course wide open is f4 with that one. I had very little hope of actually tracking my son as he swam down the lane, and timing my shot for that split second when his head came above water. And of course I was shooting from the stands, so it was a continuous right-left-right movement. It would have been ideal to stand directly at the end of the lane and take shots as he approached, but that would have been frowned upon. (Nobody said anything about the flash, but then again there were no diving events- I do know that they're much more strict for those.) Anyway, in my experience going much over 800 ISO is about where things start to break down with the K20D, especially in low light; images start to look soft, grainy, noisy- so 1250 was my limit. However, the majority of the shots were of him just standing around, or standing stationary up on one of the starting blocks, or treading water while waiting between events. I thought the equipment should've been able to handle stuff like that.
I do know that 1/250th or higher would've been desirable while he was actually swimming, but I was hoping the flash duration might be able to stop the action a bit. I also used AF-C for a while but it didn't seem to help either. I recall shooting outdoor soccer with the K20D and Tamron 70-200, and got a lot of good images in that case. I don't have the Tamron anymore but I wonder how I'd have fared using that at the swim meet. (Or a Sigma 70-200?) Locking focus with the 50-135 or 300 can be painfully slow at times.
I didn't have a lot of hope that I'd get many decent shots, given the subject activity and lighting, so my heart isn't broken. But it's just a bit annoying, kind of funny actually- people see you with this big "fancy" camera set-up and say, "Wow you must be getting some great shots!" ...Uh, no not really!
The clearance prices on the K5 right now are pretty tempting and affordable, but I figure if I'm going to upgrade, I should go all the way to the K5ii due to it's improved AF and low-light capabilities.
So I was interested in hearing the experience of others who may have used the same (or similar) lenses, while making the switch from something like a K10D or K20D, to the K5. Hopefully I'm wrong in thinking that the
lenses have anything to do with the problem.
@JinDesu, the nickname is a little irony regarding my (now ex-) wife, and a statement she once made regarding my LBA!
Thanks to everyone for all the great comments so far.