How do you properly size a speaker?


I have a 40x2 watt 4 or 8 ohm tube amp. I am very inexperianced when it comes to proper set up. I literally just bought the cheapest vintage speakers I could find with a name I knew they had no ratings i had to find that info later. I noticed some speakers have a span for wattage like 30 to 75 watts for example. I bought a pair of cerwin vega L7s for 50$ I saw that they are rated 75watt and 8ohm, there is no spectrum on the wattage that I could find. Does that mean I am running them under powered with a 40 watt amp? These are like smaller monitor speakers, would it make a difference to run the bigger floor speakers? Seems like I have seen bigger floor speakers with bigger woofers and more tweeters with wattage ratings from 30 and up? Correct me if I'm wrong I'm just curios because I will be buying a home soon and I was thinking about getting some bigger speakers when I have the room for them.
gguy767
The wattage rating on a speaker means little.  1 watt of distortion can blow a speaker much faster than 100 clean watts.
You might want to look at more efficient speakers instead of their size or age.  This is why vintage Klipsch, Cervin Vega or Realistic Mach 1's all with horn drivers can be desirable.  They can be rated around 94db to 100db at 1 watt, 1 meter at 8 ohms.  40 watts can drive many speakers to "reasonable" volumes.  Personally I would avoid anything under 90db at 8ohms.
In general, bigger speakers are more efficient and in general are able to produce more bass and sound overall off the same @ of watts.

Smaller speakers may be capable of producing similar bass levels but generally require more power to do it.

This is how it works in theory but in practice there are many factors that determine the end sound so relying on size alone can only get you so far.
I find the room and system depend on my personal taste.

Even though my floor standers are capable I use subwoofers with remote control capability as the loudness button to vary low frequency volume level and their slightly equalized presets for musical genre.

Some recordings simply don't need the low end support, so - subs off.