Thanks, Brian and Luca;
I actually bin 2x2 for platesolving, but recognize they are still big files. I haven't had any issue with the QHY 600, but the ZWO 6200 MM seems a little more temperamental.
I saw that there is a Beta version for SGP available and was hoping it would be a regular release before I used it - but a 64bit version sounds like it may help. I had some frames dropped while imaging 1x1 (1 out of 4) with the new image train and hopefully that will stop with the Beta version.