As mentioned before, much depends on what immigration office you use. When I was going from visa exempt to 3 month Non-O, Chaeng Wattana would not accept the monthly THB 65,000 for 12 months; the only two options were THB 800,000 in a Thai bank or a letter from one of the few foregn embassies that still offer this.
For any 12 month Non-O extensions, CW accepts either THB 800,000 (seasoned) or 12 months of THB 65,000.