has anybody posted the before and after results of a transient response test? I have been watching for this but never found it.
Yes, many times. It's buried somewhere in the massive DS1054Z threads. Measured bandwidth on these scopes is about 140MHz.
Like I said, I specifically watched for this and never saw any results posted. I just did another search and found nothing except for a depressing number of posts by me on the subject.
If someone wants to do this, they need a fast reference level pulse generator like a Tektronix PG506 or maybe something made from some AC logic or similar if it can be checked against a known good oscilloscope. In the case of the Rigol oscilloscopes, measurements should be made both in single shot mode and normal mode with long persistence and without averaging because we do not know how repetitive signals are processed to produce the graded index display.
The theory of 50/100MHz operation is also well understood. Dave did a "reverse engineering" video and found a switchable capacitor across the input that acts as a 50Mhz filter when enabled. It really is as simple as that.
I am well aware since I am the one who did the calculations showing the math behind the bandwidth limits.
I wish the theory behind the AC/DC coupling was just as well understood. Dave's reverse engineered schematic seems to be incomplete there.