Hi, well its a never ending quest for a good sound. (the p/u has a lot to do with it too) Steel strings are easier than nylon.
THe 500 is quite a bit bigger w/10" speakers. I like the smaller speakers a lot, i heard of a new WHarfedale 8" speaker you might want to check out.
I really like the sound of the Yamaha, but i am using the 500 amp w/the small speaker. THe 500 goes for about $999 here. You may want to rent one for a gig and see what you think.
Yes, music stores will sell you anything, tho' a good one will know their stuff.
Good luck. I think smaller speakers sound better for acoustic guitar, tho; i do a lot of classical guitar.
my web site is www.juliancatford.com
if you are interested.