Here is a quick review, I will post samples when I get the chance.
First, the 60x:
Man! This is one sweet neck pickup, if not the best I have ever had. It's not too bright, not muddy, just warm rounded tone. Sounds awesome when clean, as well as distorted. Minor gripe, the pinch harmonics don't jump out as when I used to have the 81 in the neck, but the clarity and articulation makes up for it.
Now, the 81x:
This is one freaking' bright pickup. In my Kendrick LTD (maple neck-thru construction, mahogany wings, and maple top), it is overly bright, BUT it's not harsh in any way and responds to the tone control rather well. The 81x has a ton more clarity than regular 81, and slightly more than the 18v modded 81 which IIRC is a hair warmer sounding. The 81x has a lot of harmonics although slightly harder than 81 (reg. or 18v) to produce. Overall, I'm a happy customer, although I'd have probably liked to have the 85x in this set instead of the 81x.
A final note, regarding 9v vs 18v EMGs:
Before I got this pickup set, I bought this:
It's a 9v/18v power supply, and after installing the battery shorting clip & using a stereo instrument cable, you can power your EMG pickups with that and change between 9v and 18v by flipping a switch, IMHO, just AWESOME!
Anyways, for regular EMGs (non X), and in my case the 81, the difference between the two modes was night & day. The 9v sounded like poop in comparison. The 18v sounded more round, articulate and had more clarity. The effect of 9v from that of the 18v is like adding heavy compression.
For the 60x/81x, it was not like that at all. At 9 v, they sound very nice, round, balanced, rich, but in 18v they somehow sounded dull. It sounded, to my ears anyway, as if the strings needed to be changed and/or I need to bump the gain & presence of the amp to go back to the 9v tone.
Hope this is useful, please let me know if you have questions.