I had the exact same issue. Initially they thought they could do it. But my house is old and when they did the demo they said the way they did the spacing of the supports under the wood on the older section cannot be duplicated today and the floor would never look even and the old section would always be a little higher and "squeaky". Ended up doing the whole floor. However, the hallways are old hardwood as well and the transition (via a doorway) seems fine.

Redroze, I'm just getting back online and seeing your questions, so I'll try to answer what I can. My new floor in the LR/DR was not pre-finished, it was all site-finished. I did put a pre-finished floor down in my office (no pics, sorry) because I work from home and didn't have time to be without my office for the week it would have taken to have floor sanded etc. The pre-finished does have a different feel to it than the site-finished. I wouldn't say it's grooved, just a more defined difference in between the individual planks. The office doesn't adjoin any other room, except the tiled hallway, so I didn't worry so much about the wood being different there. I see from your pictures what you mean about running the planks the same way and wanting to be sure things don't look odd. One idea might be to take up some of your FR planks, like the first 12 or so, and then put them back down interwoven with the new planks. That way there's not a clear line in between the 2 rooms, but rather a more gradual blending. Here's another couple of pictures, this time of my family room. The first one is a before shot of the hardwood floor + a rug-like carpet. The floor created a frame around the carpet. I had the carpet taken up and new hardwood put in where the carpet originally was, then everything sanded and refinished. You absolutely can't tell where the old wood was vs where the new started. In this case, the new is random width because it opens directly to the kitchen (as opposed to the LR/DR which is all the same width). So, one house, all new site-finished floors in the LR & DR, all new pre-finished floor in the office, original/refinished in the kitchen, and half&half refinished + original in the family room. Boy did we have dust! Hope this helps! New:

I realize this is an old post but wondered what you ended up going with? Considering 3" hardwood to replace carpet/tile/4" wood foyer and wondering if you are happy with your choice or if could share a picture?

My home has had floating laminate plank flooring for nearly a decade. The finish is still flawless, and I love it. It is very easy for the care routine, just vacuum and spot clean with water.