Sorry, but how will you support yourself when you are in Thailand. That's what an IO will want to know. Having an apartment lease means you are living there and not a tourist. Having, say a 12 month lease says you aren't applying for a 2 month tourist visa but intend to stay 12 months. This may worry them.
I would say if you have a brokerage account, you can use the value of your portfolio as the 850k baht equivalent. I'm Australian, and I used my Australian Superannuation (similar I think to a US 401k) balance when I applied for my O-A in Sydney.
I'm Australian too. I got an O-A. It's a little difficult to get but pretty straight forward if you follow the instructions on the web site. It gives you two years of trouble free entry although you will need a re-entry permit in the final year if you plan to leave Thailand. The main advantage for me was that you don't need funds in Thailand. You can show Australian funds including Superannuation. This gives you time to establish yourself, open bank accounts, get a lease, get drivers licences, etc without committing too much.