Flexibility of steel alloys

[jgannon]

I'm trying to make a purchasing decision on steel rods from McMaster, and I don't have nearly enough background in materials science to make the best choice. We already bought a piece of 1006, and found it to be too flexible. The other options in the size we need are 1018, A2, D2, M2/M7, O1, S7, and W1. McMaster lists hardness and yield strength for these materials, but my understanding is that these are not directly related to the property I'm interested in. Is there a chart or something somewhere that will tell me which alloy will flex the least under a fairly constant load? My gut says that the one labeled "very hard" (the M2/M7) is what I'm looking for, but I'd like numbers or an expert opinion to back it up.