can anyone tell me what a good last 600m time should be in respect to black booking this runner?

Hi Fest and welcome to the forum.

In relation to last 600m times, it is impossible to suggest what a good sectional time is.

Variables such as track, track condition, speed of the race, distance etc make determining what is a good last 600m very tough.

I suggest getting to know each tracks sectionals individually and work from there.

Cheers.