I need to be able to change 10 outputs at exactly the same time; I'm aware of port manipulation but this only work for 8 I/O pins could I use something like the && statement?
(PORTB = B11111111 && PORTD = B11111111);
(PORTB = B00000000 && PORTD = B00000000);
Any advice would be helpful.
No, the && operator doesn't do that, you need to do this:
PORTB = B11111111;
PORTD = B11111111;
The timing difference will be one clock cycle. Normal Arduino clock speed is 16mHz.
If that's too much difference you'll have to add an external 16-bit shift register.