Timing calculations on PIC18f

Hi guys,
Was exploring PIC18F controllers timing specification. Unable to understand a couple of things in time generation sequence for based on the same.

Breadboard arrangement:

MUC:PIC18f46k22

Fosc = (XTAL) = 16MHz (with 22pf decoupling)

Fcpu = Fosc/4 = 4Mhz,

Tcpu = 1/4000000 = 0.25us = 250ns

Based on my observations I have noticed the following (pls. refer to attached images):

Case 1:

while(1){

LATDbits.LATD2 = 0; //turn off led exec#0

LATDbits.LATD2 = 1; //turn on led exec#1

LATDbits.LATD2 = 0; //turn off led exec#2

LATDbits.LATD2 = 1; //turn on led exec#3

}

Observations:

Noted for exec#0 and exec#2 Time period = 500ns

After which the pin stays high for exec#3 Time period 750ns and low for exec#0 time period 240ns.

In my opinion every 8-bit instruction is getting executed every 250ns in this case, the rest of the period where the signal is high the MCU is still awaiting instructions to fullfill 4MIPS.

https://drive.google.com/open?id=0B1ujJMA_1UnySUdKMi1JeVhMUWM

Case2: (Using ternary operator)

while(1){

LATDbits.LATD2 = LATDbits.LATD2 ? 0:1;

}

Observations:

from case2 ON-OFF time period = 3.3us

https://drive.google.com/open?id=0B1ujJMA_1UnydzhQVzRwMTZONWc

Case3:

while(1){

LATDbits.LATD2 = ~ LATDbits.LATD2; //toggle bit

}