I think you should go with the 8X10

How would you place it? Should the 8' side extend to back of couch and how far should it extend toward fireplace?

It's best to get a rug that is as large as possible because that makes the room look bigger and also much more comfortable. There should be 12 to 18 inches of flooring showing around the rug. Right now your room is very one-dimensional because it has basically only one color. Choose a rug that also has some warm tones, and use those tones in your pillows and wall art for a more layered, nuanced look.

Rotate any rug the other direction and have it about 1/2 way under the sectional.

You've got a square sectional so how about a square rug? It might be nice to have the two sides of the sofa be balanced--both on the rug. To me, the side w/o the throw feels like it's not on the rug. The sofa is almost 8'x8' so 10'x10' rug?

BTW, the round table looks like a great choice. Nice proportion for this sofa and nice to add a new shape. Maybe add a colorful round table on the non-throw side? Target has this in different colors. (though it's kind of huge for a toss pillow)

http://tinyurl.com/y2rxb9vy

The rug has potential!

Consider throwing it on a diagonal and see if the geometry aligns a little better. If not, an 8x10 might be a better choice for this space.

Best of luck with your project!

Personally I would use an 8x8 area rug with this sofa.

I think the room looks like you could go a little larger.

I would tape some different sizes out on the floor with blue painters tape for visuals.

Yes to bigger rug. center the rug in the room first then position the furniture. you do have the rug running the right direction. Ideally you should have about 1 to 1.5ft wood flooring showing around the rug. No more Than 2 feet. So a lot closer to the fireplace and the sliding doors. Only the front feet need to be on the rug But the whole thing can be on the rug too. Whatever works. The more rug showing the larger the room will look. try for a walkway both sides of the sectional for better traffic flow Unless it needs to be there to allow the doors to open.

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My first instinct was to agree with "larger", however, you have a "walkway" on two sides so keeping the rug a bit smaller helps facilitate not walking with one foot on a rug and one on the flooring. btw, flooring is very nice. So, In this case, a square that fits about 3-6" past the end of the sectional with end facing the door and same perspective on the other side would work well.