Bearing ratings have almost zero to do with quality and definitely does NOT indicate how fast they roll.
ABEC is a rating for vibration in high speed machinery. They are for speeds that would be over 200 mph on skates. The closer ttolerancesrequired for the higher ratings can cause more drag in he bearings (which doesn't matter when you have a motor running a machine but does when your legs are doing the work).
A lower rated bearing from a great company can be better in quality than a high rated bearing from a poor company but within a company, the rating will generally be higher is better.
The better bearing companies (Zero Drag, Bones, Twin Cam) have some custom designs that are better for inline skating but do not meet any of the ABEC standards and they use standard (aka made by the millions and less expensive) ABEC bearings for their lower levels.
After all that, don't bother with the ratings or the bearings in your decision on what skates to buy. The bearings are the least important factor and you don't get a choice until you replace them.
The quality of the wheels is much more important, is unrated, and you also don't get a choice until replacement time.
Most important is fit. They should be snug all around the foot without pinching, especially the toes. They need to act as part of the feet.
Type of skate for the type of skating is important.
15+ years of inline skating - much longer as an engineer