The intel guys released the Arduino and Breakout boards as reference designs today .... great resource ... mucho gracias!!!
Their design choice for the SD card was the TI TXS206-29 TXS0206-29 | Application Specific (Compact flash, SD, MMC, I2C) | Voltage Level Translation | Technical documents
Guess I need to make a run into town, and pickup a UHS-1 compliant card, and see what happens.
From what I've read, that is 1.8V only, and I still do not see 1.8V voltage switching in the Arduino reference design that would make this SD 3.0 compliant as the documentation states. Certainly didn't see any magic in the TXS0206 data sheet, it just has a built in 2.6V LDO regulator for SD 1.0 and SD 2.0 cards.