Youre in the right ballpark.
I've had a few of each in several guitars through these doors - the PK is brighter, middier, sharper and higher gain but 'cleaner' if that makes any sense - its not a congested distortion, its hot as hell but its uncompressed and lets the sound of a string chime ring though. Its also tighter.
The nailbomb is thicker, but not as hot (they are similar in that regard though), meatier, more level in response, a little tailed off in the highs, so its smoother, more organic, not as tight (but perfectly capable of being 'tight', just not surgically so). Its smoother top end lends itself well to smoother, cleaner leads on the bridge, where the PK positively screams at you. The PKs high mid attack gives outstanding note definition, while the NBs blunter top end gives more percussive thunk to palm mutes.
Both clean up and roll back very well, but the NB moreso.
On the downsides the PKs high mid attack can be a little abrasive and its low end can be a bit tubby in very bassy or very acoustically energetic/resonant guitars, and the NB can be a bit brash and/or thin in bright guitars. Both work really well in an acoustically balanced instrument.
The closest you can get to a variable controlled comparison is probably one of my tracks on here in players - it uses a ceramic nailbomb on the left (smoother, tighter) and a custom pickup made for me called The Aftermath - the AM is the tightest of the 3, but its got a cleaner, chimier distortion and top end attack thats more like the PK than the NB, but not quite to the extreme of the PK; loosely speaking, to get from aftermath to PK, add mids, loosen the bass a bit, add high mid attack and crunch and un-thicken it slightly, they're quite different, but the PK is the aftermaths closest relation.
http://bareknucklepickups.co.uk/forum/index.php?topic=19791.0
