You should be reading around 325 ohms when the EOS switch opens on the -4500 coil which is the resistance across the thrust + hold winding, and 365 ohms for the -5050 coil.

The readings you've got with the EOS switch open aren't right.

See the resistance details on the coil pictures off Marcos site:

Flipper Coil 25-500/34-4500
Flipper Coil 25-500/34-5050

Is this for Lightning?

Note: the factory flipper coils according to the manual are even higher power than you have: 25-475/34-4500

Maybe consider getting coils with softer power thrust windings: like 25-600/34-4500 which according to:
https://www.flippers.com/coil-resistance.html
has a thrust coil resistance around 4.0 ohms which is close to your weaker coil.

There's other coils like: 26-500/34-4500 and 26-600/34-4500

The hold winding won't really affect how powerful the flippers are to the extent you're concerned about. You probably want to stay with /34-4500

Let us know how they go.
Does your weaker flipper have well enough grunt to get the ball up the ramps at the moment?
I also have a Lightning but it's in storage and I've actually never played it. I purchased some 25-600 flipper coils some time ago in preparation for it but they were intended for the upper playfield..

I presume airballs off those centre targets is another issue with the powerful flippers?

See post #5 here:

https://pinside.com/pinball/forum/topic/what-is-this-part-in-the-bally-1980-88-flipper-rebuild-kit

Ouch.
Carefully inspect the coil winding where the starting and ending wires cross over in case they're shorted from delamination of the wires.

It could also be the diode. If you're impatient and don't care about warranty, unsolder or clip the diode off to see if it's shorted.
Or wait to see what PinballLife says before tampering with it.

How are you finding the power of the new 25-600 coils?