That is exactly what I am thinking too. The spec for DW717 shows that it can cut up to 2x12s. However, the slider seems to be very pricy.
I'm not a mitre saw expert nor do I have one, but I have been thinking about getting one for quite a while. If I were to buy today, I probably would have bought a 12" non slider model which would be able to cut up to 2x8s. I don't think I have ever cut anything wider than 8" and if I do run into a few, I would just use a circular saw and a large 12 inch "speed square" to keep the cut nice and straight.
Just my 2 cents ...
On a plain jane cross cut, most 10's may be sufficient, but let's suppose you want to cut a shelf at 90 degrees...most of the shelves in my house are over 12". You could use a circular saw, just make sure you have a fine tooth blade handy.
Mitering at 45 degrees reduces the cross cut capacity (usually not a huge deal, however some 10's have a significantly reduced capacity as soon as you try to miter).
Cutting a 4x4 on a 10 usually involves flipping the stock over to complete the cut (and taking care to line up the blade).
Cutting tall base molding against the fence is problematic for most 10's. Even with the DW717 you have full capacity on one side of the blade, but on the other, you run into clearance issues. If you're close to the vertical capacity of the saw, I believe you need to trim it to length (or close to), then take a second pass to miter it (not 100% sure on this). Every other 10 I've seen will only do 4.75" against the fence. You could cut it flat, but it's hard to get the kind of precision you'll get out of the miter scale (you're miter scale is 4x's the length of the bevel scale). I can dial in 0.25 degrees on a miter, on a bevel I'll have a hard time getting 1 degree of accuracy (don't forget, you're working with the weight of the saw head when locking it in place). If you ask why that's important, it's because none of your walls are square. If you want tight fitting outside corners on your base molding, you'll want to use the miter scale (you would be amazed at the gap you'll see if you cut for a 90 degree corner when it's really 88 degrees).
Cutting crown is another issue.
At the end of the day, it depends on what you need. I got a 10" thinking I'm not cutting anything larger than a 2x12. I quickly learned that my limitations lie elsewhere and had to resell it and get a 12. BTW, I'm not an expert by any means. Just a guy trying to fix/improve his house. Most will do fine with a 10, but you really do have to look at the kind of work you will be doing and then choose the appropriate size saw. HTH!
