While I agree, I want to point out that SPL is also dependent on a speaker’s efficiency and not only amp wattage. There are speaker cabs that will sound much louder with 100 watts than some other speaker cabs. With an optimal multi-speaker 4 ohm load and efficient speakers, 100 watts can do a fairly decent SPL.
In general, I would recommend a 100 watt tube amp for studio and lite to medium PA support gigs and for lite non-PA support gigs such as blues, jazz, and folk clubs, but it will be vastly dependent on the speaker combination and efficiency.
In my own gig history, there have been plenty of places that I would have been very happy with a well-built 100 watt tube amp. Other gigs I wanted 1200 watt rigs, not that I necessarily needed that much wattage, but I do usually play in loud bands. Also, IMO any of those gigs would have been covered easily with a 300 watt tube amp.