bop,
Don't worry about a concrete building unless the eyebolts will be set directly into concrete. If there is any kind of intermediate wall or facing that the eyebolts attach to, there won't be any problem. And if the temperature stays with a few degrees, there won't be a problem even with a concrete building.
Cables can be rated by their breaking strength, which means that for a cable rated at 2100 lbs, it typically will break if the tension exceeds 2100 lbs. Good engineering practice (and just common sense) says that we don't want to try to use the cable at the breaking strength; if the cable is imperfect, or the load is bigger than designed, the cable will break. Please note that if a tensioned cable breaks, the result is not simply that the net falls down. There is a pretty good chance that the broken cable will whip around at high speed, and potentially seriously injure anyone in the vicinity.
So people design with a safety margin. And to make it simpler, many suppliers of cable specify a working load, which has the safety margin built in. The margin chosen for cables seems to be a factor of 2.5. That is, 840 lbs times 2.5 equals 2100 lbs. This is a reasonable margin which should cover both manufacturing imperfections, and loss of strength due to aging and corrosion.
1/8th inch cable generally is listed as 400 lbs (sometimes as low as 350) working load, and according to the calculations I posted above, that should be adequate for a 90lb net, provided you keep the sag to 9 inches or more.