230 kn TAS = 118.22m/s (x 0.514)
tan (25°) = 0.4663
g = 9.80665 (universal(ish) constant)
Thus..
R = V²/g.tan(bank)
= 118.22² / (9.80665 x 0.4663)
= 3056.29m
= 1.65 nm (divide metres by 1850 for nm)
Thus at 5000ft sHp, 210 kn EAS (giving 230 kn TAS), a 25° banked turn will give a 1.65nm radius of turn.
If you want to turn this into turn rate, work out the circumference (2.Pi.R) = 10.37nm. At 230 kn TAS you would fly around this in (230 / 10.37 = ) 0.045 hours, or (x 60 x 60 = ) 162 seconds. That's 360° in 162 seconds, or (360 / 162 = ) 2.2°/s.
I'm sure that there are rules of thumb for all this, but being an engineer I live with a calculator in my hand anyway - and tend to use it for my flying too (I confess to struggling in CAA / JAA exams because I'm totally unused to the Dalton computer, and suchlike tools).
G