A DM3 is the last of the older matrixes, looks like this;
It's a fair bit bigger and the bolt is a little more complicated than the DM4 which was a revolutionary upgrade when it first came out in terms of size, eyes and the bolt being less parts that all thread together as opposed to separate bits that have to be inserted in the right order. The DM4 was originally a high-end and still performs as well as any Matrix, just a bit bigger and heavier.
If you do go for the DM4 you'll be fine with a revvy, which can feed 11 bps happily and with the eyes and the ability to tune the gun so the bolt will bounce off paint will keep you free of chops etc. The one problem you'll have will be air efficiency, with less shots than some from a bottle, but if you get around to getting a good 1.1L 4500psi bottle you can use it on any guns you buy in the future so it's worth spending the money in the long run