Socrates coined the phrase: Know thyself. In this case, it can be modified to: Know thymount.
How heavy you can load it depends on how smooth it's tracking is and how that changes with payload weight and weight distribution. Long exposure astrophotographers, who measure exposures in terms of hundreds of seconds, find that loading a mount to 1/2 of the rated payload gives better odds of not having a wiggle or jiggle than the odds with more payload. So this "rule of thumb" may or may not apply to your situation. Each mount and payload has its own character. Just like individual people, you have to get to know the mount and learn what works.
For EAA, exposures are measured in terms of 10s of seconds or less. The odds of having a tracking hiccup are much lower with those small durations. In addition, you can set a FWHM filter in SharpCap to discard smeared subs. In the worst case, just start over because you aren't dealing with hours of integrated exposures. You are likely dealing with 5 minutes. So while the basic principle behind the 50% rule applies (keep the weight down to increase your odds of getting good subs), the load limit that achieves this for a 10-30 second exposure may be higher than 50% of rated capacity.
What happens at a dark site, stays at a dark site... Just like Vegas, it's all about the odds.