Single Precision vs Double Precision
I am a little rusty on my architectures currently, but I believe the single FPU unit is configured with a bit width wide enough for Either full bore calculation at double precision for one core, or two cores at single precision. Which is similar to Intels Hyper threading. OR there was something along the lines for that in reasoning.
Anytime you do double precision floating point the load is going to be higher regardless, FPU's have always been a pricey and complex part of CPU's.Under efficient use other logic calculations and math can be used that are more efficient use of cycles than making pure use of the FPU for some things.