Yes the 664 was basically the 464 but with disk instead of tape. The 464 had red and green extra keys while the 664 had blue and the cursors were different shape, but other than that, they were the same machine, and yes the 6128 had a single whole keyboard while theothers had seperates cursors and numerics.
Im sure the 6128 had the cursors positioned on the lower of the keyboard cos the others had them on the upper half.
Oh and yeah, 80 column screen meant the Display was superior and made it ( the disk based amstrads ) a vastly superior business machine than any other 8 bit in my opinion. ( Sinclair QL anyone ? - LOL )
The Basic language built-in to the CPC was indeed amazing and very powerful.
I would also like to add that the built in Basic of the CBM16 and the Plus/4 was also extremely powerful.
I might add, that I was very much into the Commodore over the Amstrads and while I did have a play with the basic, I never truly go into it all that deeplyand so I wont argue which one is better, but, if I had to chose one, then I would say that the Commodore was superior.... Not the VIC range, that was awful, just the C16&Plus/4.
MSTE @ 16Mhz : 4MB+8MB : Magic & Jinnee
TT030 @ 32Mhz : 10+16MB : Magic & Jinnee
Falcon060 @ 95Mhz : 16+512MB : MiNT & Jinnee
More PCs than PC World has... Probably