The thing about lockstep is it's straight up luck of the draw, and is VERY sensitive to network conditions, since it's essentially brute-force networking.
Things that can determine your input lag in lockstep:
- Wireless internet versus wired
- How many network hops between all players cumulatively
- Open or closed NAT
- Bandwidth congestion (someone else downloading or torrenting)
- Ping, cumulative between all players (this is the thing that really makes or breaks lockstep)
All I know is in one of the Bungie podcasts, they said Reach's netcode takes up significantly less bandwidth than Halo 3. I'll play it safe and say it was a 40% reduction, although I might have heard 60%. The ability to have someone drop out wouldn't add any noticable lag, you're still just networking buttons and they were still using Halo 3's netcode for that, which was their first successful attempt at campaign networking. (They tried it for Halo 2, but it had to be pulled)
I've had awesome Reach sessions, and Reach sessions with 3 second delays on input. Same with ODST. It's all in the environmental variables. I'd go into the tradeoffs between lockstep and asynch if you're interested, but I do need to go and clean the kitchen in the old apartment :lol