I run around 55-56 in the 400 consistently, as a strength-based endurance guy (4:32 in the 1600), and going out sub 60 always led me to blow up and run 2:06.
Interestingly I ran 2:05 at the start of the season by splitting 63, 62.
Now I'm sure close to even or a hint positive is best for endurance ppl, so I think my optimal splits would've been like 61-62 and then a 62-63 for 2:04 or so, but I never got to run it. Time trialled 600m as part of workout reps later in season in 1:28.
I tried the three different strategies (negative, even, positive, in that order) in the 800 on three consecutive weeks which resulted in pretty similar times. Was convinced I'd run much faster going out hard but maybe I was just hitting a wall due to my limited speed. I'm not sure how much running the 800 30 minutes after an all out 1500 affected my recovery on those races, but I wasn't willing to try it fresh.
Race 1: 59.2-58.7 (got a clean break in after the stagger, smooth ride drafting in lane 1 all the way swinging wide only in the homestretch to pass. Not sure what my 200 splits were)
Race 2: 59.0-59.1 (a bit more jostling for position on the first lap than I was used to, mostly 29s the whole way though.)
Race 3: 57.8-59.9 (had to swing wide twice but nothing crazy. First 200 was a bit aggressive, 27.xx which likely accounted for my slow down, as I had to back off to recover)
I always felt like basically even was best for me
Here were my splits (estimated from a video) for a couple of my PRs:
1:59: 30.3, 30.5, 30.6, 27.9
1:53: 28.3, 28.5, 27.9, 28.7
Positive splits will forever be the only method to run a truly speedy 800M. The rest are just tactical.