Keeping an A4000 or an A3000 is a tough choice. 
That's why I call on you my friends, my helping hand, in my time of need /Brandy *not Groove Armada*
sigh, sorry been a though day
I have both. The A3000 is very solidly built, has built in scsi, flicker-fixer. It's biggest problem is ECS, not a big issue now if you get a graphics card. Oh and you'll need to mod your board if you want to use the UWSCSI on a CyberStorm Mk3.
Mendark
I like the fact it's solid idd. I got a spare CV3D so ECS is not a problem and with flickerfixer so the A4k's output is neither a problem. Confusing.
If you manage to use the C=3640 in your A3000, you'll need to get a daughtercard for your A4000. You might be able to pick up another daughter 3640 of the 030 one that came with the 4000/30.
My idea was to just switch them. So the A3k got the 040 and the A4k get the 030.