PORTB's advantage is probably moot, since we are throwing in delays anyway. The only advantage is to eliminate those microseconds of delay when setting two ports simultaneously. However, the difference is not trivial - is about 95 times faster, according to John Boxall's blog: PORTB | tronixstuff.com
However, using PORTx commands introduce a lot of risk, reduces portability and readability and should be avoided unless truly needed.
I just wanted to see if I could get it working and I will NOT be using PORTx for a stepper application.