Re: Speaker response
This is why instrument speakers are different from stereo or "hi-fi" speakers. Hi-fi speakers are made to replicate the original sound, so they have a flat frequency response. However instrument speakers on the other sound are made achieve a certain tone. Just like with anything (pickups, amps, etc) all guitarist desire different tones. All speakers are different. As far as I've tried, Jensen speakers tend to have more midrange and treble response with less bass, and Celestions are typically a lot warmer. Also, Jensens are usually associated with Fender style amps while Celestions, etc., are used in more british type of amps like Marshalls, etc. Also warmer speakers can be used to tame brighter amps and also the opposite.
What you want from you're guitar amp is totally up to you and there is a HUGE variety of speakers so that you can find what is appropriate for you.