Truxton has samplerate 450 so not possible to use optim mode there either.
7Mhz dotclk (according to https://pineight.com/mw/index.php?title=Dot_clock_rates)
7000000 / ( 270 * 57.6 ) = 450.10288
Is it normal for OSSC to report the number of lines and refresh rate inconsistently? For example trying this again I get 269 lines and 57.78Hz.