I think the statement in the manual that says "It is basically half a PULSIN", is refering to the operation of the commands, not the resolution of them.
PULSIN has to see both edges of a pulse, RCTIME only needs to see the trailing edge.

Both commands have 10uS resolution with a 4Mhz oscillator.
And DEFINE PULSIN_MAX places the same limit on both commands, which is the number of "Periods" until it times out.

But really, since you are using interrupts ... measure the pulses with a Timer, or the CCP module.
Let the Hardware do the work, and your program can be off doing other things.