Re: how loud is an orange rockerverb 50?
so, the general thing about wattage and volume is that you have to add a zero to get twice as loud. If you have a 5 watt head and want it to be twice as loud, it'll be a 50. twice as loud as that? 500. And so on. The problem is that your Marshall head is a 100w, and the math just doesn't work out easy. The closest thing I can suggest is to buy 10 Tiny Terrors and run them on half wattage. That should get you in the ball park.
If there was a solid correlation between power amp RMS wattage ratings and dB levels (other extraneous variables such as speaker efficiency, humans being most sensitive to midrange around 800 Hz - 4K Hz, bandwith, etc complicate the matter) you're forgetting that decibels are logarithmic. For example, the difference between 97 dB (a very general maximum level for 15W lunchbox amps) and 103 dB (very generally levels for a 100W Marshall half-stack) is
only six decibels right? The amplitude for 97 dB is ~70.8K units, while the amplitude for 103 dB is ~141K units. So that "small" difference between decibel levels produces roughly double the amplitude (at these levels, an increase of 70.8K units is very much significant) with the function
f(
x)=(20)log[SUB]10[/SUB](
x), where
f(
x) is the decibel rating and (
x) is your amplitude. Now that six decibel difference between 60 dB and 66 dB would have amplitudes of 1001 and 2001 respectively; a small change of 1K units.
The Rockerverb 50 would still be a monster though. If your goal is tinnitus, it can deliver.

If you have the chance, try both and see if you think the higher price for the mk2 is justified. Though simultaneously keep in mind, "Buy once; cry once", and get whichever one you really want to avoid any buyer's remorse.