Fastest way to toggle a bit in ASM

You could try the following using an XOR:

movlw 0x01 ; move 0x01 to W register
xorwf lat, F ; XOR W with port & store result in port latch

An exclusive OR operation will preserve the values in bits where the bits in the working register are set to zero and invert the values where it is set. So you could also use the same technique to toggle multiple bits.