Re: little JB jr vrs full size JB
I have a lil59 and a full size 59 in 2 different guitars but they are the same kind of guitar.
2013 Charvel San Dimas Hard Tail has the Lil59
2016 Charvel San Simas Hard Tail has the full size 59
I know this is not the JB but I think this might be what your asking about just with a different pickup
The Lil59 is flat out fantastic and destroys all single coil pickups I ever heard or used. It's fat and full like the full size pickup but not quite as good.
As said above it is different but IMO it's more of the same then different. The Full size 59 has a warmer fuller tone. The Lil59 has the same sonic signature but with slightly less output.
When I play both guitars VS style, I can hear the difference in them. It's not much as the smaller wonderful Lil59 really takes the place of a full size hum bucker without having to cut your guitar or plate to install a full size hum bucker. I think this idea of smaller single coil size pickup replacements for single coils is the way to go in guitars originally with Single coils. They sound better have more output and are quieter. It's the next best thing to the real deal my friend.
If I owned a Strat again, I would fully load it with Lil style pickups or Hot rails which are another wonderful pickup instead of single coils.
Honestly I fully HATE single coil pickups for what I do. I'm a heavy Metal guitar player and there is no place in my playing for single coils. I think they sound thin, crappy and noisy. I can't think of any good reason to own a single coil pickup when Seymour Duncan makes killer mini hum bucker style pickups that sound so much fuller , richer and have better output then any single coil on the market that I have heard or played. I don't know if they exist so this is just my personal 37 years of playing guitar speaking.
I use 250k pots for my mini hum bucker guitars. 500k pots I don't think sound quite right to me anyway. I never messed around with a 300k. I'd call Seymour duncan and explain your future setup and see what they suggest you replace your pots with or if the 300k's will get you where you want to be. I'm thinking 250k but I could be off in your tonal quest.
I strongly suggest trying out the JB JR, I have 3 guitars with the full size JB's in them and they are probably hands down my favorite pickup due to its incredible flexibility. I adjust the poles in mine to get me the flavor I'm after in said guitar. I learned this little trick that really enhances the abilities of the JB pickup. It goes from awesome to incredible with just a few turns of a screw driver. Pickup height is probably a overlooked tweak many might not see as a tonal enhancement but it can really make a pickup go from mild to wild.
Report back as I'm interested in what you do and how your digging the JB jr. I really dig the new Strat's that just came out Elite I think they are called , that new Blue color caught my eye and I want to go try one out. I can see a JB jr going right in.