I used an aluminum T extrusion on the X axis and bolted that between the maker slides. I have no sag and not enough flex or twist to measure. I'm running a Dewalt 611 for my spindle. I supported the Y axis with L brackets like Earwigger did https://discuss.inventables.com/t/thoughts-on-stiffening-mod/12174/11?u=lewisbyerly>
There is really no such thing as an "average" job. I can cut up a 24 X 24 inch piece of Mdf into parts for 3 by 3 by 5 inch boxes in 20 minutes. Carving a 4 by 5 inch picture into a piece of maple can take an hour. Like Shane said it all depends on what your doing.
One thing you need to be aware of is that this really is a build it yourself project and it will take some adjustment to get it to work properly. If you are careful and choose your mods before you start ( I did the stiffening and changed the way some of the wiring was done during assembly ) you will greatly cut down on the "take it apart and start over" headaches. When you get stuck Inventables customer service is great and the forum has advice on everything you can think of about the machine and plenty of people willing to help.
I have had almost no trouble with the machine and use it just about every day. I couldn't be happier.