The effect of sulfa antibiotics on the world population roughly 20 years earlier will not be as great as some people think. While antibiotics in general are a very good thing indeed, the major increases in lifespan and particularly in maternal health/mortality and infant mortality and mortality in children up to five is NOT due to antibiotics. Clean water and sewage disposal, proper nutrition, vaccines (which won't arrive much sooner if at all with sulfa drugs earlier), birth control, etc all contribute more to a population bump than antibiotics. Improved crops and farming techniques for nutrition. Having said all that you will see an increase in population compared to OTL but I'm not so sure that will mean a huge wave downstream - when conditions improve, folks tend to have fewer children as you don't need so many spares. Antibiotics, or at least sulfa drugs 20 years early, are not enough to lead to "soylent green" by the 60s/70s or even now.