tbone4523:

Please don't build your top out of 2x8s. They are full of knots, are flat sawn from relatively young trees, and will not remain dimensionally stable no matter the finish.

Generally one can cantilever 1/3 to 2/3. I'd say 17" is close enough to the 20" you'd need to cantilever 10".

Yes, you can box up the top to 40" high.

I built a bar height counter with a 12" overhang. It is 23" across, and sits on top of a total 10" of a brick faced, framed half wall and a Soapstone backsplash, which it overhangs another inch plus on the kitchen counter side.
It is supported at one end where ties in to the window ledge, and on the other end it is notched into a 10" wide post. It is 5' long with no supports in between, and very stout.
Depending on the thickness of your material, (mine is 2.25" thick), you might need to add a couple corbels, or brackets just to be safe...

Thanks for the help, to be safe i think i might build 2 L brackets into the knee wall and anchor the top to the end wall. Any recommendations for a relatively inexpensive wood top 62 x ~30", I won't be doing any cutting on it as its main function will be a "bar", I don't have alot of tools so custom build would be tough.

I really like the look of your countertop ctycdm something like that is what my kitchen needs!

I just saw a great article in TOH January 2013 - Page 73 about using stair treads to create an island top. Standard rounded edged treads on each side, then straight pieces in the middle. They ripped the rounded edge off the ones in the middle, then used biscuits and glue to put the top together.

Just a thought.