I think the main reason why I'm so delighted that Frankel will race as a 4-y-o is that he is still obviously maturing and thus improving too and his owner thankfully can afford to let his love of racing and his desire to see the horse fulfill it's potential outweigh the immediate financial rewards.
Brigadier Gerard was the best miler that I have ever seen and he achieved a Timeform mark of 144. I would not be at all surprised to see Frankel surpass this next year should he stay sound.
The highest rating that Timeform ever awarded was 145 to Sea Bird II, winner of the 1965 Derby and Arc.
To put these ratings into context, Sea The Stars achieved a rating of 140.
Ten years before I was born but I have heard it said that Sea Bird was just amazing. I would like to see them send Frankel to the Breeders though. Beat the best everywhere.