[Startrek (Martin)]

After using DSS for 4 years I’ve never had a stack that took longer than 30mins or so to complete ( with up to 4 or 5 hours of data )
Today it’s taken 2 hours to stack 160 subs with another 140 to go
Seems unusually long and never experienced this ever before ?

Camera is the ZWOASI2600MC
Stacking details -
300 x 60 sec subs ( 50MB fits ea )
40 x Flats ( 50MB fits ea )
40 x Bias ( 50MB fits ea )
DSS version 4.2.5 64 bit
Kappa Sigma clipping
Use all available processors checked
Star detection found 50 stars
Plenty of storage space in main and temporary ( 400GB )
i7 processor 2.60GHz
16GB ram
64 bit OS running Windows 10 Pro
No virus protection disabled
No notifications disabled
No updates disabled
Totally autonomous Laptop

I registered and stacked the 300 x 60sec light frames on their own without calibration frames and it took 30 minutes ?
How could adding calibration frames quadruple the stacking time ?

Any ideas or suggestions or tips to speed up the process
??
Admittedly I’ve never ever stacked any more than 120 subs previously over the 4 years ( firstly with a DSLR and in the last 14 months with the 2600MC) mainly because subs have been 90 sec to 300 sec +
I chose 60 sec subs due to galaxy imaging in Bortle 8 skies with Neigbours flood lights lighting my backyard up like downtown Las Vegas

Thanks