Help choosing a camera for fast shots
What you're asking for would probably give a $5,000 camera kit a hard time, and the SD card isn't really relevant if your camera's memory buffer and card bus are slow. Why be cheap and more difficult? If you have a client who wants dog photos, do dog photos the right way. I'd prefocus where the jump would be and just take one frame, instead of playing Spray and Pray. If that's what you need to do, however, get a nice telephoto lens, a dSLR, and a tripod, and bill appropriately.
I do not think a 5k camera setup would struggle. But I suspect that was for dramatic effect. Or perhaps you meant if you use a 5k setup poorly the results will still be poor.
See link below for what I'm shooting....
It spits back... "This content is currently unavailable." Don't use Facebook for photos that you want the public to see. Get a Flickr page, a PBase page, or something similar intended for photo sharing.
Or use the gallery function here.
What you "want" is a fast DSLR with a sports lens. The shutter speeds you will be using will mean you are unlikely to need a tripod. Although it is never a bad idea to have a monopod or better still a tripod. A tripod is better, but if you have to move and setup a couple of times, a monopod is going to be much more convenient. I have both, and use them alot (especially the tripod) just not when I am shooting fast moving things.
If there are known point of interest and you will be shooting there, then pre-focus is a good idea. If not it includes shots in multiple locations then pre-focus won't be super helpful.
Since dog shows (in my limited experiance of showing two a few dozen times) tend to be outside and in relatively good light (with the bigger ones in well lit interior locations) you do not need a camera like the d5100, where the main sellng point is how super good it is in low light. The same with the Pentax, also the pentax has a very poor selection of sports lenses and so is not the best for this type of work.
What I suggest is a Nikon d300. They are a little older, but still really nice pro level cameras. They are still even with the top of the line Canon gear in this same class (7d) when it comes to low light performance, dynamic range and color sensitivity. The 7d adds a nice movie mode among other things.
A used d300 would be slightly less then a new d5100 (based on local prices here in Norway, your local prices will naturally not be identical). Just make sure you get one with low shutter actuations (the fewer shots taken the better, photoshop and several online sites can count actuactions from a JPG). Next you need a sports lens. The best would be to get a 70-200vr assuming you will not be closer then 15-20 feet (for framing) If you are going to be very close a Sigma 50-150 f2.8 would be best, with a Nikon 24-120 f4 VR as a reasonable (but more expensive) alternative. Since you sound like you have a tighter budget, instead of a 70-200vr a Sigma 70-200 f2.8 bought used would be a good choice. It won't match the results from a Nikon 70-200vr (or a Canon 70-200is), but it is much cheaper. The other option is the previously mentiond sigma 50-150mm. Again suggesting used as the newer model costs much more and adds stabilization which you won't need.
Shooting fast movers like running dogs, you will not need VR or IS. You will need a higher shutter speed to freeze the action. A monopod imight help you to start with, since your technique is likely to be bad (wild swings, and unstable camera handling seems to be the rule with new to DSLR users). And once you get good technigue down you can try without. I shoot a lot of sports and similar things and generally do not use a tripod or monopod for those types of shots.
For lower light shots you are going to have to push the ISO. I do not think dogs would deal well with a highpower flash and a beamer. Perhaps most of them would have enough discipline to not freak, but there would be at least 1 or 2 complaints per show.
Why a d300?
You can not buy a faster focusing and better motion tracking camera without spending many 1000's of dollars more.
The sensor (for its time) was revolutionary and as a result is still near some of the best cameras available.
It is rugged (well built) with exceptional ergonomics and ewll thought out control placement.
It has a super nice viewfinder (you'd be amazed how important this becomes).
Only Nikon and Canon have a wide selection of sports lenses.
Why the Sigma 70-200?
It is in response to your budget concerns. I MUCH prefer the Nikon 70-200vr. The Nikon has better image quality, is weather sealed, faster focusing, and so on... But the Sigma is the best thing going in the next price class down. Below it the only real option is the Sigma 50-150 which while fast is generally not going to be long enough.
Do not get a bridge camera like the fz150. Not fast enough to get reliable results. This relates to focus speed, shutter speeds available, ISO levels available and so on. Even a minor dip in the lights and you will see significant levels of ISO noise. Also a brdige camera is a larger SLR looking camera but except for the Fuji x-s1 bridge cameras use the same sensor as the smaller cameras but with a more compromised lens.
I do not think you will get acceptable results with anything less than an SLR. If you decide you prefer a Canon to thed 300, consider a used Canon 50d. It does not match the d300 in speed or lowlight, but it is still a very good camera with very good ergonomics and a nice control layout and a nice viewfinder.
See my plan (in my profile) for what I shoot with. See my gallery for images I find amusing.