I recently carved this 28" x 25" x 2" art piece out of poplar on my Shapeoko XXL. It took a total of about 10 hours on the machine, using a 3/4" roughing end mill, a 1/4" for intermediate adaptive passes, and finishing off the details with a 1/8" downcut end mill - then a 1/4" Vee bit for some engraved details. I did some preliminary sanding, but am waiting to get my Dremel tool back from a friend to really clean up the edges and then I estimate 3-5 hours of hand sanding to really clean it up.
I must add that using downcut end mills has saved me hours on sanding and prevents a lot of chipping too… If you haven’t tried them, I highly recommend them!
Another note on my process is that I have begun using smaller stepdowns lately: usually .07" to - .09". Of course this increases cutting time, but it tends to give cleaner finishes and less chipping. Most importantly, it gives me peace of mind, not constantly listening for an abrasive sound when the machine cuts an unexpectedly deep or aggressive section.