It mainly depends on whether you want to tie up 800k baht (almost untouchable) in a Thai bank account earning about 0.5% interest, or commit to transferring 65k baht per month from overseas (the better option of these two as you can spend every baht of the 65k as soon as it's registered in your account) OR whether you want to demonstrate money in an overseas account (usually equivalent to 800k) earning a much higher interest rate (in my case I use Supernannustion funds earning around 7% tax free). The money I make from the super fund so very easily covers the cost of a decent health insurance policy, which is a requirement of the OA. Once the original 12-month VISA (not the entry stamp) is almost at expiry you step over a land border, step back in and get a further 12 month stamp (no need to visit an immigration office to beg for an extension). At some stage during the period of that entry stamp (the later the better) you fly back home, spend a bit of time with family and friends, apply for a new OA and repeat the process. You transfer only as much money as you need, and never have to visit a dreaded immigration office. You get two years from the one visa
OA is more worthwhile if you visit your home country every 22-24 months and do one strategic border bounce just before the visa expiry date, getting a new OA in your home country each visit. No need to transfer money and can use home country insurance. Also never have to apply for an extension, so no visits to immigration office required.
There's no correlation between the 65k/month or the 800k. The difference is the 65k belongs to you exclusively to spend how you want. The 800k just sits in the bank gathering dust. It's a no-brainer
The 800k method is a total misuse of money. You don't ever see it again as long as you stay in Thailand. I need 45-50 a month to live anyway, so jacking it up to 65 is no big deal. And it's mine to spend as soon as I get it