I have not had any crashes in testing my latest versions. Atmospheric drag should add almost no performance hit or instability. Planetary re-entry causes some lag but it's very simmilar to the lag you get when you crash large ships. It is due to lots of blocks being damaged at once.

Think about it like this.... If crashing your ship into an asteroid would cause lag then tossing it into the atmosphere to burn up will cause about the same amount of lag

thanks for your reply!

though, is there any information on performance on local or internet servers? (dedicated or otherwise)

Currently there is an inherent problem in the space engineers code with using a certain function to apply forces to grids on dedicated servers and in multiplayer if you are not the host. Therefore, the drag code will not work on ships that are currently being piloted while playing multiplayer. Re-Entry effects will still work and drag will work on ships if they are not currently being piloted. Other than that there is nothing in the code that should lag or slow down the game noticeably in multiplayer but I wouldn't recommend using it for multiplayer because of the issues stated above.

Thanks. Maybe over time and updates, this post can be updated for the latest on stability and MP status?

Also, Im sortof hoping they add your features to the main branch, and since theyre always trying to go for realism-esque, might not be too far fetched ;D