I'd say with 99% confidence no home audio speaker can handle a program of 4x their power rating. Physics states that a speaker can handle a peak power of 3x its rated rms power.
The real question is what methodology are manufacturers using to come up with rms power ratings? Ideally, 20hz-20khz pink noise should be used. Your assumption about using sealed speakers is not so cut and dry either. If you have a speaker with a port tuning frequency of 30hz pretty much everything from 50hz down to 30hz is going to consume very little power compared to other frequencies and there will be very little cone excursion and significantly less power consumption very close to the tuning frequency because of the way the port becomes a resonator. I once owned a pair of very large pair of ported speakers that were tuned to about 25hz. I ran them full range with the lfe going to them and noticed very little excursion during super bass heavy scenes and they handled it just fine even at reference volume.
A bookshelf speaker tuned at 60hz might handle rock music just fine at very high levels but be destroyed by dubstep at the same volume.
Its always a good idea to get more amplifier power than you need even if your speakers aren't rated for it. If your amp has a maximum peak power of 85 watts and your speakers rms rating is 85 watts a simple 3dB increase will send the amp into severe clipping. Generally, tweeters only consume about 15-20% of the power of the speaker. Tweeters are not rated for the same power handling. You might have a speaker rated at 100w rms, but that woofer might be rated at 150w rms and the tweeter 20w rms. if you're pushing 100 watts into the speaker and the tweeter is getting 15 of those watts as soon as you run out of headroom you just showed the xover an infinitely high frequency at the clipping and all that power is now dumped in DC mode into the tweeter, which has an Xmax in fractions of millimeters and significantly less power handling than your woofer. Guess what happens next?
The second question, and more important one to ask when deciding whether your amplifier and speakers can give and take enough power is how loud are you going to listen? Let's assume you're listening in two channel mode, your speakers are rated 87dB 1w/1m and your room is not acoustically dead. Even sitting 16 feet away 100w gets you 99dB. For music, this is excessively loud. For theater at reference level, we can add in the center channel, I'll give the surrounds the benefit of the doubt of not contributing much to the sound. Now you got 101dB, 4dB short of reference but still incredibly loud regardless.
People put way too much emphasis on watts, both output and power handling. People in the audio community are always going on about how many watts this receiver outputs, or how high of power handling this speaker has, when they should be asking "How effective is this speaker at converting electrical watts into sound?" It's much cheaper and efficient to think about sensitivity. If someone needs more spl, it's much effective to get speakers that are more efficient. If you replace an 87dB 1w/1m bookshelf with a large 95dB 1w/1m floor standing speaker, guess what? You've just gained what would have taken 400w of power to achieve in an equally sensitive speaker. If you stack two subs next to each other rated for 200w you've effectively gained what would have taken 800w in a single sub with 400w.
