Hi Alistair,
Good chocie on the JM's mate, fantastic gear!
The main difference betwen the Powerspells and the 3 Kings rods is the tip strength vs Butt Strength...
Both rods have the incredible fish fighting parabolic action to the blanks that JM is famous for, but the 3 Kings special was designed to fish lighter jigs, with a more sensitive tip, while still maintaining the incredible butt strength of the heavier Powerspell models.
In a nutshell, this means you can fish jigs in a slightly wider range effectively, while still maintaining the low end grunt to horse big fish off the bottom.
If you are looking at fishing a broad range of Jigs, say from 200 grams up to 400 grams, then the 3 Kings 300 would be awesome. 300 gram tip sesnitivty with 500 gram butt strength.
An equivalent 500 gram Powerspell woul enable you to fish 400 to 600 gram jigs effectivelt, but would not be great to use with lighter jigs as the tip section would be too stiff for lighter jigs to be worked effectively... It would work of course, but wouldn't be the perfect tool for the job on lighter jigs...
Of course if you are going to be plumbing serious depths of the Kenyan Rips, and be needing 400 to 600 gram jigs 99% of the time, then the Powerspell would be the better option.
I would suggest one of each, with the 6000PG matching up to the lighter of the 3 Kings specials, and possibly a Powerspell 400 to match to the 10000PG...
But personally I would go for 1 x 3 Kings Specials 300 for the 10K... 1 x Powerspell 200 for the lighter work.... the 200 will handle jigs from 150 right up to 300 grams, and be an awesome set up for mid weights and depths...
Tough choice, and perhaps I've confused you further with my ramblings, but I hope this helps!
Cheers
Andre