I only run 140w to that little one, and it sounds fine. Though my speakers rely on the HU, so we're not talking about a high powered system. Basically, if it can rattle a license plate, it's too frigging loud for me. Clarity is what I pay for, and I've almost achieved. Still loud enough I can't hear other traffic or my exhaust when I want. You can get more powerful 8's that will deliver more punch, but I have no need for them.
That said, it plays audibly down to 35Hz. 8", no matter the make or model will start to have trouble under 40 for the most part, mine starts to fall off from 40 to 35 where you can't hear it anymore below that point. 10 inch will fill to a little under 30 Hz, perhaps down to 25, and 12 or larger will carry you to subsonic should you want it. Of course, each takes up more space than mine, and is why I opted for the 8. Low enough for most of the music I listen to.
Other odds and ends about 8 inchers in sealed enclosures: Rap sounds a little odd as the little drivers are tight, so the loose flappiness of rap bass gets lost and a bit distorted, but for the chillout and electronica I listen to that has a lot of tight bass tones, it sounds great! Beautiful for kick drum and low down bass guitar in rock tunes as well...