Trust me, you can't brick a nook. I did something far worse than you--I deleted the entire partition table of the NT and I still recovered it with a bootable SD. Make sure the LVM and bootable flags are set if you used gparted to flash the SD image.
Nook Color running CM7 Mirage, no gapps, Nook Tweaks app @ 1.3GHz (+500MHz past stock 0.8GHz)
Nook Tablet running CM10.1.3, no gapps, BexusNv4 kernel @ 1.3GHz (+300MHz x2 past stock 1GHz)
SGS2 T-Mobile (unlocked) running HellyBean 4.2.2, no gapps, @ 1.72GHz (+~200MHz x2 past stock 1.51GHz)