The A4000 is pretty basic.
It's a 68030 at 25 mhz and 16 Mb ram.
A 4gb HDD and a DVD-reader.
It also has a Peggy Plus card in it, that's a mpeg card that can play mpeg movies in hardware.
And it is running OS 3.9.
I'm using it mainly for retro-gaming, but i'm planning to upgrade so i can throw out my PC's and use the amiga as my main computer.
The A1200 on the other hand has a Viper 1230 at 40 Mhz and 32 mb ram, so the A1200 is now actually faster than the A4000.
But i'm planning to upgrade both of them, but it seems to be hard to find accelerators and stuff for the A4000 (at least not as easy as for the 1200).