Windows 8.1 Store app background task throttling limits under concurrent async requests

Goal

I am designing a Windows 8.1 Store app that issues several concurrent WinRT asynchronous operations (IAsyncOperation) while the app moves between foreground and background states. I need to understand the documented limits on how the OS schedules these operations so I can decide how much parallelism is safe to rely on.

Constraints and uncertainty

My understanding is that Windows 8.1 aggressively prioritizes the foreground app and can suspend Store apps, freezing their threads to reclaim CPU and memory. It is unclear to me whether in-flight async operations are completed, cancelled, or deferred when the app transitions to the Suspended state, and whether background tasks have a hard CPU or wall-clock quota that would look like latency under concurrent load.

I also cannot tell from the documentation whether the NTFS I/O queue introduces additional contention when many async file operations run at high queue depth, or whether that throttling only applies to background-tagged work.

Questions

• What are the documented CPU and time quotas for background tasks in Windows 8.1, and do they differ from Windows 8.0?
• When an app is suspended, what is the guaranteed behavior for pending IAsyncOperation instances?
• Is Windows Performance Toolkit (WPR/WPA) the supported way to confirm OS-level throttling versus app-level latency?