Oversized is still oversized, but the issues involving efficincy and comfort will be reduced, but you won't get the full benefit of the modulating furnace in more mild weather.
Oversizing the condensor is still bad if it's a 2 speed. You'll lose out on the full benefit of the system and not remove as much humidity. There are some arguments for oversizing a heat pump slightly, but not an A/C.
Proper installation and ductwork sizing also affect comfort... and are commonly one of the problems with oversized equipment. Bigger furnace = more airflow. If the ductwork is too small, it will be noisy and not distribute the air evenly.
It's pretty hard to undersize equipment. You would only notice undersized equipment on the coldest 3 or 4 days of the year, and hotest week of the year... and that's only if you use a large setback at night. A system thats sized perfectly will be running constantly on the coldest day of the year and hotest day of the year to maintain temperature... and the A/C might fall behind if you are opening and closing doors frequently or entertaining a large number of guests in the middle of hte afternoon.... but you will still remove the humidity effeciently so it will "feel" comfortable.
The reason people oversize HVAC is the same reason they "need" a V8 vs a V6. you could probably place a recording device on engine of most cars with the larger engine option and will discover that it only see's the top 20% of the enignes capability perhaps once per week at most... and that probably wasn't even nessesary. The downside of course is higher purchase price and higher operating costs.