If you want a predictor while also working on speed endurance, overspeed technique, metabolic efficiency, and form maintenance under high levels of fatigue, then you can run either 500m run, 100m walk, 200m run or 600m run, 100m walk, 200m run. Add 4-5 seconds to the final 800m time (same pace for the 700m total) to obtain an accurate prediction.
A closer prediction that will more closely replicate race conditions, but speed will be reduced are the following two workouts:
500m run, 100m jog, 200m run or 600m run, 100m jog, 200m run. This setup should accurately predict your final time, but will vary based upon the speed of your 100m jog portion. A conservative prediction is to add 1.5-2.5 seconds to your final time.
Predictions are difficult with rests that fully or nearly fully restore creatine phosphate levels (2:30 for full restoration). A peaking workout I used for the 800m is 3x200m with a jog across the infield rest (1:30) that ended up averaging 3 seconds faster than 400m pace, so 27's for you. Focus on incorporating 150's as an addition to the end of your workouts of 4-6 with a 1:30-2:30 jog rest to work on technique, turnover, speed development, and extension of your creatine phosphate system.
Try 4x400m with 2 minute recoveries for a very accurate predictor that tests your capabilities completely.
Your 100m aligns well with your 400m (superior performance) while a significant gap exists between the 400m and 800m (almost 10 seconds). Balanced training should yield a 6 second gap per lap for an athlete with strong endurance (3k, 5k, 8k). A 4 second gap is possible for an endurance trained athlete; however, your makeup shows more proficiency at the 400m with a similar 100:400m ratio that I have observed before. I would suggest focusing on endurance to close the gap down to 6-7 seconds, rather than the current almost 10 seconds.
I would think you may be able to attain a slight PR to 2:21 with perfect pacing and execution, but you should experience significant slowdown and form breakdown with extra energy required for inefficient movements at the 1:30 point of the race (point of full aerobic energy contribution). Shorter repeats will hide this deficiency's full impact, rather than improving it to minimize the performance impact. Longer repeats like 400m-600m and higher volume (up to 2400m for primary portion of the workout w/o added 150's) will assess the metabolic and muscular demands of the late stages of your race.