I have several questions about amp speaker sizes, and it would be greatly appreciated if you'd help me out=]

first off, what is the difference (in terms of tone and volume) between a 1x15, a 2x10, and a 4x10?

secondly, I was looking at ashdown amps, to be specific the MAG series, and i noticed that the MAG C410T-300 and the MAG C210T-300 both have a 300 watt output. How is this possible? Shouldn't 4 10" speakers be twice as loud as 2 10" speakers?

my last question is also about wattage. Is it possible that two amps with 200 watt output could have a different overall volume while being used with the same amount of ohms?( sorry if i phrased that incorrectly) I ask this because while i was playing with two amps of the same wattage at the store i noticed one sounded noticeably quieter at full volume. (and yes i used the same bass.)

I know thats a lot to read but id really really appreciate it if you helped me out. Its totally fine if you just want to answer one or two questions, and im especially interested in the last 2.

thank you soooo much in advance for any help you give me!=]
The 1x15 has more boomy lows, and may come off as muddy (that was more down to my EQing) the 2x10 has the mids more pronounced than the 1x15. and the 4x10 is the same thing basically as the 2x10 just more punchyness. Check the third post here and it should answer your questions better
As for volume, it comes down to watts for actual volume, but I believe people tend to perceive higher frequencies as louder.

as for your other questions, I'm afraid I can't help because I'm not familiar with heads and cabs