Perceived volume is a strange thing. If it's all fundamental, it won't develop properly in the room, but the folks next door will have their fillings falling out.
Perceived volume is a function of four elements: 1) the efficiency of the driver as coupled to the cabinet; 2) watts, watts and more clean watts; 3) the frequency spectrum over which the power is distributed, and 4) the room and its resonances either reinforcing or detracting from #s 1-3.
So, for example, you can have a 100 watt head, but if you don't have it coupled to an efficient cabinet, it won't get any louder than a 10-watt head that has the most efficient cabinet there is, an so on.
The best thing to do is research on the efficiency of any particular head and cabinet combo for your application. That's why, even though it is bulky, I still have my 17 year old Carvin 300 head and SWR Triad cabinet. It has the efficiency and the bandwidth with the power necessary to carry any gig I need, from jazz trio on this side of the board to slab high-dB rock-n-roll gigs on the other side of this board, and why I still keep a Marshall 100 watt head for the rare times I play guitar. It's not that I turn it up that loud, but I've tried gigs with smaller combo amps and I have run into the same situation with just not being able to keep up with anything less.