The difference between the two devices is the cellular bands that they support. The Global variant (RM-875) includes support for LTE 845MHz, 900MHz, 1800MHz, 2100MHZ, and 2500MHz (bands 20, 8, 3, 1 and 7 respectively). The US variant (RM-877) includes support for LTE 700 MHz, 850MHz, 1900MHz, and 1700/2100MHZ (bands 17, 5, 2 and 4 respectively), which would suggest it is headed towards the AT&T network.
The RM-875 device has a similar aerial layout to the Nokia Lumia 920, although there's an additional aerial location labelled as "LTE7 MIMO" (possibly an addition to improve LTE Band VII performance). The main cellular antennae are at the bottom of the device, one for the high band frequencies, and one for the low frequencies, and are supplemented by the high and low band MIMO antennae on the left hand side of the device. The GPS antenna is on the top right of the device, and the Bluetooth/WiFi aerial is just down from the top right corner.
The dimensions listed (130.35mm x 71.4mm) are also similar to the Lumia 920 (130.3 mm x 70.8mm), but a little bigger than the Lumia 925, which would tie in with leaked pictures of the Nokia "EOS" that show a Nokia Lumia 920 sized device.