Because of some of the functionality of the ASUS TF701 it's difficult to make a comparison. It is fast for what it does but as was mentioned the Nexus line is pure Android so there is no bloat. But you also give up the keyboard/dock option and microSD card slot not to mention a great stock backup app.
Like I said, for pure performance the Nexus would probably be better but the ASUS has more features.
How does the nexus compare to the nvidia tegra 4?
In answer to your question, "Is the Nexus 10 the powerhouse of 10" tablets?" No! Qualcomm has unveiled their Snapdragon 805 tablet, and it’s probably some of the most advanced hardware ever put in an Android tablet. The tablet, which runs Android 4.4 KitKat, has Qualcomm’s unreleased Snapdragon 805 processor on board, which looks to be a quad-core CPU clocked at 2.7 GHz. You’ll also get 3 GB of RAM, 64 GB of internal storage, a 2560 x 1440 display, a 13 megapixel rear camera and 2 megapixel front camera, and a slew of standard radios and ports, including 802.11ac WiFi radios, Bluetooth 4.0, GPS, NFC, a microSD card slot, an HDMI port, and a USB port.