When CPC started their free delivery on everything, it was pretty fast. Usually next day. Really no different from their paid for delivery, or free above a certain value. But not for long.
Ordered up something well above the old limit for free delivery last Friday and it still hasn't arrived.
So it looks like they're recovering the cost of free delivery for small orders by using a cheaper and slower service across the board, unless you pay extra for next day or whatever.