Performance gain by implementing streamlined simplex
By "streamlined", I assume you are talking about a minimum cost flow algorithm, and you have been using the standard LP solver from Coin-OR. Then I would advise using the solver from the Lemon library (from Coin-OR as well). It has Python bindings.

As for the performance, I never benchmarked it myself. Given the algorithms involved, however, just the datastructure specialization may well be a 10x improvement. For some problems, I guess the difference may well be orders of magnitude.

I don't think Coin-LP detects the network structure - I'm pretty sure neither it nor GLPK does.

There are algorithms specialized for transportation problems (even more specific than MCF), but here you'd probably have to reimplement them, and not gain as much as going from generic simplex to minimum cost flow.

While looking for benchmarks, I just found two other solvers linked from this blog post, with performance claims: Google OR-tools and PyMCFSimplex.