And, yes, generally the easiest path to faster performance is just loading everything into memory and working with it there. In my PDF script I need to validate that the ID numbers are being read are valid, so I pull all 20,000 of them and put them into a HashSet<String>. That's extremely fast to validate with compared to an array and performs a bit better than a HashTable. There are times when I need to use an SqlDataReader or StreamReader and read row by row or line by line (4 GB+ text files suck), but that's only when memory has become a problem.
I've been meaning to really dig into the High Performance PowerShell with LINQ article (https://www.red-gate.com/simple-talk/dotnet/net-framework/hi...), but I just don't have a need for it at present unless I refactor an existing script and they all work great.
i mean, if the code is 90% I/O bound i agree: micro-optimisations can be a waste of time. But tight, nested loops that are only memory bound i think is worth the effort.. so for me, if i need need to do a lot of field comparisons for 300k accounts or groups from AD, i will download the ad data into memory and use foreach(), hashtables and generic collections wherever possible.. i actually think were making the same point anyway. I now reach for C# before powershell for situations like above where performance matters, but powershell does have advantages for smashing out some quick work. But i honestly cringe when i hear people talk about powershell scripts that take minutes to execute for tasks that should be reasonably quick.