CF Memory Card Recommendation for Nikon D810

I've just now ordered a D810 DSLR and realised that it has a CF memory card slot. Coming from a D5100 and D7100, I am only use to SD cards. I am shocked by how expensive these CF cards are compared to SD. I am aware that the D810 also has an SD card slot. My questions are:

1) Why would Nikon not use 2 SD slots like in the D7100?

2) Can I use just the SD slot and leave the CF slot empty? or do I need to fill in both slots?

3) Is there any point in buying a 120MB/s or 160MB/s CF card if my SD card can only reach speeds of 80/90MB/s ? I understand the camera is only as fast as the slowest card.

4) Due to the massive sizes of the D810 NEF files, I would want a 64GB CF card. Which has the best price/performance? The Lexar Professional 64GB 800x Speed 120MB/s CompactFlash interests me.

The D810 has both CF and SD slots. Yes, use whichever you prefer, or both. CF is the good stuff, a little faster than SD, which is why. Don't cheap out at this point. Cheaping out is NOT the FX way.

Writing one Raw file now and then is not a big deal, time-wise. Writing a continuous burst of ten files is a much bigger deal.

I use Lexar 1000x CF on a D800. It can write five 40MB NEF (200 MB) in about three seconds. It will do more than five, I just never bothered. I think the D810 is supposed to be a little faster.

1000x is 1000 x 150 KB = 150 MB/second, however, the advertised speeds (1000x or 90MB/second, etc) are Read speeds, possibly achieved by your card reader and computer (which is rather important when downloading a few hundred files). For sure, you want a USB 3.0 card reader.

Write speed is NOT that fast. But my D800 and 1000x doing 200MB in 3 seconds is about 67 MB/second write.

I use the Sandisk Extreme Pro CF card. I bought a 32mb size, runs at 160mb/s. I use a Sandisk Extreme Pro SD 32mb card as my overflow card.

You do not need to fill both slots.