Test set and benchmarks for linear programming I am searching for test instances and benchmarks for linear programming, in particular, when solved by a simplex method and implemented with floating-point arithmetic.

This includes test suites, to verify my implementation of the simplex method, and benchmarks to measure the performance. The performance measure relevant for me is the number of steps on the vertex graph, rather than absolute clock time. Therefore medium size instances that do not induce to much ill-conditioning would suit me best.
The standard reference is probably Hans Mittelmann's page. Note, however, that the number of simplex iterations performed will depend on the pivoting rule and how the code deals with degeneracy.