Not to step on any of the Guru's toes here, but I can try to explain the answer to your question.

Most people don't really know in dB what is "loud".

Here is a list of common noises and their decibel levels:

• Aircraft at take-off (180)
• Fireworks (140)
• Snowmobile (120)
• Chain saw (110)
• Amplified music (110)
• Lawn mower (90)
• Noisy office (90)
• Vacuum cleaner (80)
• City traffic (80)
• Normal conversation (60)
• Refrigerator humming (40)
• Whisper (20)
• Leaves rustling (10)
• Calm breathing (10)

 So for us, we want to try and get close to that of amplified music give or take a few dB. (most people can't tell a difference of <3dB btw)

Every 3dB increase requires 2X the power because dB is a logarithmic scale not a linear one.

So you only need 1W for 87dB, 2W for 90dB, 4W for 93db, 8W for 96dB, 16W for 99dB, 32W for 102dB, 64W for 105dB, 128W for 108dB, 256W for 111dB.

BTW 105dB is pretty loud to me but may not be for you.

:)

Yeah I agree with bootman, I wouldn't get too hung up on the power rating spec, especially considering that there are quite a few tricks that manufacturers can use to make it appear you will get more power from an amp than you would in reality.

However keep in mind that those sensitivity ratings are for when you are one meter from the speaker, so SPL drops off rapidly the further away you get from the speaker.  

In any event, I have heard our 5Ts with the Peachtree Nova and I thought it indeed sounded pretty nice.  To my ear they sounded great, and I thought that they could push the 5Ts to around 90 dB with no problems when I was about 10 feet away, which is also quite loud in my opinion. 

Using the same calculations that bootman did with 80 wpc and a 87 dB speaker at 3 meters you would run into clipping around 96 dB or so.  

I hope that helps!