Agree you will need a decent graphics card for your 2000. ECS and AGA for that matter are just to slow with a large palette and high resolution.
For a 2000 a nice Picasso II or Spectrum are decent budget choices. Never ran them on a 68k system though.
For Z3 systems a CV64, BLT Z3, or Picasso IV are nice solid choices.
A good graphic card will make a much bigger improvement than a faster cpu.
