That's where quality of infrastructure becomes important. When you're designing a portal system, there are a number of infrastructure issues to be considered. The design of your network, placement of servers, and type of hardware will all affect bandwidth and throughput. The good news is that you can almost always get the bandwidth and throughput you want, as long as you're willing to spend the money. The relationship between throughput and cost is roughly linear - the more you have the more it costs.
Stability refers to how often the system is down, either unexpectedly or planned.
The telecommunication industry rates stability by a scale of nines. I doubt anyone in student affairs needs a four nine system, but a two nine system is worth shooting for. Scalability characterizes the ability of a system to grow to meet demand. We generally talk about it in terms of the number of simultaneous users that can be handled. A scalable system will allow you to build an installation that can handle 10 users but easily expand to handle 10,000 without having to redesign the whole system.