Regarding the proof of balance, there are some privacy concerns, but if there is really demand for it I will pass the request along. In the meantime I can assure you that we keep all customer funds secure.
What concerns me is that you are offering such high limits while calling 5 BTC cashouts large. What if someone came to your site and placed a lot of NFL bets? If they had a good run they could easily win 1000+ BTC. Does your site have anywhere near that kind of reserves to sustain that type of variance? And if not why are you offering such high limits?
It was supposed to mean "larger than before" and not necessarily "large". We can assure you that also higher payouts are no problem - we are just very careful with automated cashouts. In fact some of our customers already won more than 100 BTC. Keep in mind that you are always betting against another customer, who already deposited all funds you can possibly win.
For our main market makers we also have a different rule regarding the reserving of funds. They can put as many open orders as they want. The funds will be deducted from their balance before a bet is matched. If the market maker does not have enough funds, we will NOT match the bet.
I passed your request along for a proof of balance and still waiting for an answer. I will get back to you asap.