The performance meter looks to be very stressable. I'm curious where the limits are setteled. Probably at 650 pieces it turns red? I shall make a "tutorial" about this.
Why would you make a tutorial about something before you understand how it works? The meter measures
performance, not object count. In forge, performance has always been based primarily on how many objects the game must render at any given time, with additional strain coming from things like explosions and other particle effects. If even a tiny portion of an object is visible to a player, that player's console must render said object inits entirety. Some objects will place more strain on the hardware than others based upon things like polygon count and detail (items with lights and glass were harder to render in Reach, for instance), but the raw number of objects rendered at any given time is the biggest factor here. Another thing to take into account is the game's impostering system where objects "imposter out" for less detailed (easier to render) versions at a distance. This means that at a distance, despite the player potentially having more objects in view and therefore rendering more objects at once, there may actually be less strain put on the hardware.
Now, that is how performance has worked in the past. This forge is based upon a modified version of the same engine, so there's no reason why it shouldn't work this way now. However, the way the meter reads performance is unclear as of yet. First of all, the meter is active in forge, meaning that it can not account for all of the player models, projectiles, and particles which are rendered in-game. However, there are several types of forge objects (respawn points, hill markers) which are invisible (are not rendered) in game which the meter is taking into account. So, this meter won't be a perfect representation of performance, merely an indicator. We'll have to see exactly how it reads performance once we get the game,
then we can think about tutorials.