TFW2005 Interview

All stars of ACToys.net has done some first-class sleuthing to give an indication of the rough size of Masterpiece Grimlock in robot mode compared to Masterpiece Optimus Prime and Classics (Henkei) Optimus Prime. It is a fascinating and well thought out process, and although it may not be 100% accurate, you can see from the images that Masterpiece Grimlock will be approximately a head shorter than the Masterpiece Optimus Prime.

https://news.tfw2005.com/2008/10/15/marcelo-matere-interview-166286