There are two major battery manufacturers that Hobbyking.com sells. They are the Turnigy and Zippy brands. I spotted the Zippy 8000mAH pack that would fit inside the front hub shell of the Tidalforce hub battery, but am now having second thoughts since they seem to be overrated in terms of their C rating and they also have higher internal resistance than Turnigy packs. This was discussed in the following Endless-sphere.com thread.
I'll investigate further, but it looks like I'll have to revisit what I can fit inside the front hub! Unfortunately, it looks as if Turnigy doesn't sell a 5S 8000mAH battery. The largest they have in 5S is 5000mAH. Sigh.