Both the tablets are powered by 2.2 GHz Snapdragon 800 processor with 2GB of RAM. Both the tablets are offered in 16/32/64GB storage variants. Amazon claims that both the tablets can run for 11 hours with mixed usage.
Kindle Fire HDX 7-inch
Kindle Fire HDX 7-inch as a screen resolution of 1920 X 1200 pixels (323 PPI) which is equal to that of Google Nexus 7. This model is about 303gm in weight and has 8mm of thickness. This tablet has HD camera at front of unknown pixels. 16GB Wi-Fi only model comes with a price tag of $229.
Kindle Fire HDX 8.9 inch
As compared to 7-inch tablet 8.9 inch model comes with a higher screen resolution of 2560 X 1600 pixels which makes up pixel density of 339PPI. This model has weight of 374gm and thickness of 8mm. 8-inch model comes with both front and rear facing HD cameras where rear camera is of 8 Mega Pixels. This model is priced at $379 for 16GB Wi-Fi only model.
Availability
As far as the availability of the tablets is concerned, 16GB Wi-Fi only model of 8.9-inch tablet will ship from November 7Th and 16GB 4G LTE model will go on sale from November 14th. 16GB Wi-Fi only variant of 7-inch tablet will go on sale by October 2nd. You can pre-order both the tablets from today.