You need to allow for mains voltage tolerance (230V -6/+10% or 216 to 253VAC), transformer load regulation (the toroid spec I just looked at was 5%), and a lower volt drop over the bridge rectifier when zero load.

So taking a 33VAC toroid, applying 10% more power (mains voltage here is at the higher end of tolerance) gives 36VAC (we'll round for simplicity) at rated load. Add 5% load regulation, which means we bump our basic unloaded voltage to 37.8AC.

Multiply by root 2 (or 1.41), gives us 53.3VDC. Take away a little bit volt drop for the bridge rectifier, and we have in the region of 52VDC.