Now.......I'd rather test at 100, then based on the results, try it out at a longer distance. Keep up with what groups good and your ES and SD. Even if it groups great and the ES is terrible, try it at longer ranges so you know, and the opposite. Bad groups with great ES, try them out too. This is just my opinion...... if the load is consistently bad a shorter distances, it will not get any better at longer distances.
The issue with testing at longer distances is the wind. If the load has horizontal spread at 100 and and 600, it's the load. If the horizontal spread is good at 100 but not 600.... is it the wind? It's very common for the wind to pick up and die down a bit........ this can confuse you with bad horizontal spread. Sometimes you get lucky and there's next to no wind, but that doesn't seem to happen very often for me! If you're fortunate enough to have a longer range close by, then you can probably find days when the wind if favorable to try it out.
I'm going to do some testing one of these days, but I have some old load data when I used my Competition Electronics Chronograph that had GREAT SD and ES. I've been using the LabRadar for a couple of years now, and I just can't seem to get the same great SD and ES as I did with the Competition Electronics Chronograph. Sometimes I will get a ES of 60 fps or so, but the load usually still groups very good. If your ES is bad and your vertical spread is bad at longer ranges, your chronograph isn't lying to you.