Hi Greg,
We regret for the delayed response.
I am afraid that I was not able to reproduce the issue "Thread aborted" when we use 5000 rows with copy style and ApplyMarker. Also I have a simple sample and it is available in the below link:
http://websamples.syncfusion.com/samples/XlsIO.Web/5.2.0.25/I38292_1/main.htmPlease have a look at the above sample and if still the issue exists, could you please try reproducing it in the above sample and send us the modified sample so that we could sort out the cause of the issue and provide you a solution?
Best Regards,
Melba