Mills in this price range are not all that dissimilar. One of the biggest difference's would be 4 or 5 axis.
In addition to this it become a question of support, optimization and integration.
For instance, CAP Complete includes 3Shape, Sum 3D CAM and the Roland. You can check out all the features here.
CAP Complete - Integrated CAD / CAM Solution On the 3Shape side we have developed a world class anatomic library. This dramatically improves the quality of the contour you design, in addition it gets you to this final design using fewer mouse clicks.
The CAM (Sum 3 D) has been optimized to use a 0.3mm tool to go through the anatomy providing the detail that that's included in the library. Most mills smallest tool size is either 0.6 or 1mm.
On the milling side we have found great award winning zirconia (CAP FZ) and worked out a multi coloring process that is included in the training when someone buys from CAP. The zirconia is made in Germany and is very price competitive as long as you don't compare it to zirconia made in China. This is rounded out with PMMA in every vita shade, wax for casting and or pressing and a white for diagnostic wax ups as well as tools.
Another significant difference is Roland's 2 Year guarantee. Most mills are 1 year.
The last item is support. CAP currently has 3 full time support staff with 2 additional people that back up in the support area. We will likely be adding a 4th full time person in the fist qtr. 2013. Our support goal is to answer every call as it comes in and we track the metrics of this in addition to tracking the all problems until resolved.
I really didn't mean this to come off as a sales pitch, but many of the differences in mills priced in this range are more about the company you buy from than the actual mill. In conclusion it's really about optimization, manufacturer guarantee and support. Lastly, I believe mills manufactured in Germany, Japan, and Switzerland are generally know as having the best quality build.
Hope this helps,
Happy new year,
Bob