If you like the sound of single coils in 60s position, I'd keep the WL. If you need to go low, you can use the D-tuner. Will Lee himself even sets it to drop to a low C.
The 24F5 won't sound like a 60s single coil instrument, even with Nordstrand Big Singles. Both pickups of the 24F5 are closer to the bridge than on your WL. The 24F5 would cut through like mad, but would sound very modern compared to your WL. There's just something about that pillow a 60s single coil instrument can deliver.
You could always save some money, sell your WL4 and order a WL5...
