Hope this image works...



Here is a size comparison between the plush Optimus I got from eBay (on the right) and the larger sized plush Optimus I found at Luna Park (on the left).
The plushies Griffin saw must have been the larger sized ones.

For anyone looking to get them, you can purchase them from one of the clown games at Luna Park but they are 3x the price of the smaller ones from eBay. The day I went they had several Optimus and Megatron in both modes and a few Bumblebee's too.