The main problem here is that the question is ill-posed. As I've been saying here for years, "think SPL, not watts!" A given sound-pressure level can be achieved as a result of an infinite combination of amplifier power and cab sensitivity. The room also matters a great deal. Furthermore, as has been mentioned, given that it's a specific level one is after, there's no such thing as too much power, just adjust to the desired level. Most of the comments above about watts, etc. are just plain misguided and stem from inappropriate generalizations that, admittedly are often useful but can be misleading.
Here's an example. Suppose you take that recommended 100-watt amp and pair it with a cab that achieves 93 dB SPL @ 1-meter with 1 watt (a realistic spec). Now instead, you choose a cab rated at 100 dB SPL @ 1-meter with 1 watt (another realistic spec). All other things being equal between the two cabs (frequency response, directivity, cone excursion, etc.), the SPL achieved with the first cab at 100 watts will be achieved by only 25 watts with the second cab. Every 3 dB increase in sensitivity means a reduction in required power by half. Now, of course, all things are rarely actually equal. There may be reasons why you want that less-sensitive cab. Given many of the cabs out there, the 100-watt recommendation would be a good starting point but it may not work well at all. Not considering what's really behind all of this has led many to waste a great deal of money.
Really though, no offense, but the entire premise is folly. First of all, as has been mentioned, there's more to emulating the sound of a DB than simply achieving a given level. Second, there is no specific level that represents a DB. After all, many of us amplify our DBs as a necessary evil that stems from practicality. Most of us would prefer to go unplugged.
