Performance testing terminology

I'm writing some testing documentation and have described performance/load testing where I'm running high traffic as large numbers of concurrent users (this seems to be most commonly what is meant by performance testing).

But I also want to ramp test the system's performance by function: if I, for example, upload increasingly large documents, what size document finally breaks my app? Or open a search's parameters too wide, how many results can a query be expected to find before it times the system out.

What would the correct term be for this second type of testing? It seems to lie between functional and performance.

Thanks