Std velocity rounds are quieter, noticeably less unpleasant to shoot without hearing protection. In my 16.5" barreled rifle, I chrono ~1250 fps with almost all the regular HV rounds (Golden Bullets, Mini Mags, Federal HV, etc) which is almost exactly what the box says. Cci Std velocity runs ~1080. Less energy, but it makes little difference on smaller creatures at close range. I can't speak to roo hunting (kangaroo, I assume?).
All that said, my rifle shoots certain HV rounds extremely well, which led me to pile up a bunch of it. Some of the std velocity also shoots very well, particularly CCI std velocity, but it is more expensive around these parts, so I lean toward the cheaper HV stuff.