10-12 reps will be 5km race pace or a touch quicker. 
If you want to increase the tempo for all or part of the session then skip every second or every third rep.

Start at any marker near Swan Street bridge and head towards Anderson Street. After one minute stationary recovery, run in the reverse direction. Regroup at the same spot before starting the third rep and so on.
Alternate session: just do 4 reps or shorten the last pair (eg 60 or 90 secs).

1500/1250/1000/750/500/250 (2 mins approx. stat rec)- note new recoveries below.

Start at the pillars. Run the 1,500m out towards Anderson Street and up the hill. About 100m from the top, opposite the gates to gardens, will be the 1.5km marker. Stop and rest until 8.00 after the start. The 1,250m ends just before Government House Dr. (2.75km marker). Now rest until 15.00. Start the 1,000m from the uprights over Government House Dr. and run until you have completed a full lap of the tan. Rest until 21.00 then run the 750m out towards Anderson Street (750m marker). Rest until 25.30. Run the 500m back towards pillars (250m marker). Rest until 28.30 before doing the final 250m back to the pillars.

Meet at the Pillars, jog to Anderson St. 
Run 10 x 200m hills with a jog down.

Recoveries are 3-4 mins / 90secs-2 mins approx.

Meet at Pillars.  Every Odd Rep commences at Pillars and uses the 250/500/750 markers following an 'out and back' pattern: 
2 x 250 w/60 secs Static Recovery (SR)2 x 500 w/75 secs SR2 x 750 w/90 secs SR
2 x 500 w/75 secs SR  2 x 250 w/ 60 secs/2 mins SR.
1 x 750 (jog return).

This session is 5 sets of out-and-back reps. Start each set (i.e. odd rep) at the Pillars.1) 2 mins clockwise, wait for 60 secs, return. Re-group at the Pillars. 2) 4 mins anti-clockwise, wait for 60 secs then return. 3) 1 min clockwise, wait for 1 min, return. Repeat twice more. 

Options: (a) skip a set or two to reduce total volume.  (b) increase the 1 min reps to 75 secs (and take only 45 secs rec) to focus on endurance rather than speed.