Realistically, how fast can you go on strides? 800m pace? 400m pace?

That's all that matters.

If I was feeling good, I sometimes clocked rolling 100m strides in under 12s. Let me tell you, I was never gonna run a sub 48 400m

I don’t think strides are the best 400m indicator, it’ll put you in a ballpark considering you did multiple after a fatiguing run and likely short rest, but to run 52-53 in a 400m the bare minimum speed is around 12.0.

For reference, when I ran 49.high, my coach had us doing a workout where we’d jog 300m slow and then sprint a straight, and I was clocking 11.2-11.4s while my 46.high teammate was getting 10.8-11s.

I agree but you'll be much fresher after a 3 mile shakeout than at the end of a day's worth of mileage, especially if it's a couple back to back days of moderate mileage (think 10 one day; 3 and 8 double the next day). I'd almost never run faster than 13.0 in a flying 100, though I was intentionally holding back a decent chunk, and ran 51.6* (hand-timed but with confirming video) in a time trial.

best thread on some time

If they were comfortably fast, does that mean it felt like you could have run 53.x right then and there? Also, what do you think your flying 100m would be if you ran all out and well rested?

You seriously went to the track to run some strides versus just banging them out on the road?

Hobbs does 40m strides in 4s to work on mechanics/top end speed/power output.

You can do whatever you want. You just have to

1) have a reason to do the chosen effort & duration/distance

2) understand the consequences of your choice with regards to how the power output and duration might affect your body/set requirements for recovery before your next session

I always felt like 800 pace was way too fast for strides. 1500 pace feels just right. But I mostly prefer doing 150s/200s over 100s, if you're doing 50s then there's a place for 400/800 pace as well.

I always run my strides barefoot, so I’d never do the on the road. Grass (or astroturf) only.

I think doing several 100m strides at 400m pace would be about as fast as a person could or should do them. Faster than that and you're basically just sprinting. Depends a bit on what kind of runner you are and how many you're doing, but I would say somewhere between 400m and 800m pace makes more sense, likely building up speed a bit the first 30m and maintaining it the last 70m (running start). If you're not an 800m specialist, doing 100m reps at 800m race pace is still decently fast running for most distance runners.

I guess in my mind, it's more about perceived effort and making sure you're running relaxed and with good form. When I describe strides to people, I say it's like doing short sprints at somewhere between 90 and 95 percent effort, making sure you're cruising but not straining at all. Whatever that looks like for you should be good. Full recoveries between reps.