Looks about right.
The limits of the 150Mhz Rigol probe are very clear (see image). The 300Mhz harmonic is definitely attenuated by it.
I've measured the bandwidth at every configuration, I get:
70Mhz DHO800: 125MHz measured bandwidth
100Mhz DHO800: 200MHz measured
125MHz DHO900: 225MHz measured
250Mhz DHO900: 280Mhz measured
This was done using a pulse fed into the 'scope via. 50 Ohm terminated coax and measuring the rise time.
Martin72 has confirmed the math (ie. 0.45/rise time) by measuring attenuation of signals from his signal generator.
(my cheapo siggen doesn't go that high...
)
Why is Rigol so conservative with the labeling? No idea.