I had both a stock '030 and a stock '040 A4000 back in the day and found the A4000 with the '040 a lot snappier as a whole.
That being said, I was never a big gamer on my Miggies, but general usage wise the '040 machine was a lot nicer to use.
The stock 3640 cards are pretty cheap these days, so not too costly of an option if you want a bit of a bump up performance wise.
