If you're creating a Multiplatform game how do you know that system can handle it?

Hi, i'm wondering if how you can know that that system can handle it, for example you create a 3D Sidescroller with weapons etc, do you have to use less objects in one area to ensure you're game runs stable or even setting the graphical objects of you're game or maybe even Multiplayer.

Multiplayer Third Person Shooter Example PC:16 Players (Changable graphical settings) IPad:12 Players (Low) IPhone:8 (Low)

Also how much players can play online on differnent formats. I heard it was 50-60 on PC Using Servers but i don't know about the IPad or IPhone.

Thanks for reading

Once you have an iOS developer license you get access to the XCode development tools, one of which is the iOS simulator, which simulates performance of iOS devices. You can then run your game in the simulator to see how it performs.