Risky, you should take a look at users photos. There are plenty out there. The noise seems to be controlled very well at ISO's below 800. ISO 800 is decent, but not that pretty. You will get a printable 4x6 image, but you might not be able to enlarge it much. ISO 1600 is kind of messy, but most UZ camera's at ISO 400 are just as messy.
If you are interested in capturing "indoor" action, then I believe high ISO capability will be more useful than IS...hell, it will help better than a tripod! Because IS will not help stop the action, only a faster exposure time will...which can only be done by increasing ISO (or by adding more light!)...
And that is where the external flash will help.
I feel like I'm trying to sell the S5200. I actually own an S2 IS and I can personally vouch for the useability of IS in preventing camera shake. I can often take sharp photos with an exposure as slow as 1/8th second when at full zoom. Without IS, I am doomed to an extremely faster exposure. Indoors, this usually forces me into a very dark exposure. This also means that the S2 IS can take very sharp images at exposures that will not be able to stop action (hence subject blur, but not camera shake). Here's an example of what I expect you'll see (lol):
With the S5200, there is no IS...But, raising the ISO can help you by allowing you to use a faster exposure to produce a still properly exposed image. And because using a faster exposure means helping prevent BOTH camera shake AND subject motion, this is where I put my money (I've got 50 cents) for indoor action. UNFORTUNATELY (ya, in caps), because the S5200 doesn't have IS, you might very well be doomed into keeping the zoom to a minimum, or else you might find your images blurry due to camera shake. Though, I'm guessing that if you can get a fast enough exposure to stop the action, you'll have a fast enough exposure to stop camera shake.
All the possible scenarios are difficult to walk through, and I don't own an S5200 (or any camera that is ISO1600 capable) to help illustrate the differences or validate my opinions...
If you find a place that allows returns, that seems the thing to do...though I don't like the idea of people buying camera's with the intention of returning them *shrug*
Oh, and finally...The Fuji does not really produce cleaner images at the lowest ISO value (50 for the S2). It just controls noise better at all other ISO values.
I hope I made sense. I hope I didn't say anything that isn't true. I hope it helped.