Going to max with roach hydra vs roach infestor is an easy way to lose a game. The timing of roach/hydra attacks are very thin vs roach infestor -- there is a reason you very rarely, if ever, see roach hydra used in competetive games. Hydras are simply too slow to get into position fast enough to compensate for the fact that they're made out of paper.
Generally, at 200/200, adding hydras to your roach/infestor ball (and I mean a small amount -- roughly 8-12) is a good idea, as they can sit at the back of the concave and fire away. However, trying to say roach hydra is equally as strong is a complete lie -- roach infestor gets into position faster, dictates where the engagements happen and has a better ability to transfer (infestors are retainable for a switch into broodlords, ultras or other tier 3 -- roach hydra, not so much).
Even the smallest donations help keep sc2sea running! All donations go towards helping our site run including our monthly server hosting fees and sc2sea sponsored community tournaments we host. Find out more here.