It is kind of a mystery. Wattage ratings in heads is sometimes more marketing than science. There are 22-watt amps like the Fender Deluxe that sound way louder than its 22 watts. Then there are Class D amps that claim to be 1000 watts that can barely get over the drums. If you are additionally pushing the 5150 with a boost/overdrive, it would increase the output. I would say go for it if you were playing at bedroom volumes. If you plan on cranking the amp, as you said, there is a good possibility you could blow a speaker. I like my cab to be at least 1.5x my amp. For example, a 150-watt cab for a 100-watt head. You could use the duo for years and never blow a speaker, but yes, there is a chance you might. It all depends on your tolerance for risk.
I recently upgraded my 150-watt Marshall 2x12 cab's speakers when I bought a 120-watt head. I might have been fine, it is all about what your tolerance for risk is.
