I'm aware of the usb to serial comms limitations between the Pi and Arduino Mega board on my printer, and when printing complex curves at higher speeds, the printer stutters and blobs.
I believe the Mega 2560 is an 8 bit board.
So question - if I upgrade the ;printer board from the Mega 2560 to a BigTreeTech SKR V1.3 32bit Controller, will the comms between the Pi and the 32bit printer board be faster, and fast enough to prevent the stuttering.
The print direct from SD card is currently giving a much cleaner and faster print, but I really like the control and convenience that OctoPrint gives.
Upgrading from an 8 bit controller board to a 32 bit controller board may help with the stuttering but it isn't a guarantee. The stuttering can be caused by the 8 bit board not being able to process the commands fast enough but it can also be caused by the serial bandwidth not being high enough to get the commands to the controller board in time. Since you say that the files print better directly from the SD card, I would guess the serial bandwidth is causing your issues.
One solution that has been working for many people is the Arc-Welder plugin.
Converts G0/G1 commands to G2/G3 commands. This can greatly compress some GCode files and can reduce the number of GCodes sent to your printer when streaming GCode from OctoPrint. This can reduce stuttering as long as your firmware correctly implements G2/G3 (arc) commands and is configured properly.
Most 8 bit Mega 2560 boards are capable of running Marlin firmware with G2/G3 support. You just have to determine if your firmware has the support.
I am very tempted to upgrade to a BigTreeTech SKR V1.4 Turbo 32bit Controller ( very little difference in cost to the 1.3 ).
Motivation for the upgrade is to convert X & Y axis to the BIGTREETECH Closed Loop Driver S42B V1.0, so reducing the possibility of missed steps ( had 2 minor cases of skips in the last month, and both in the middle of the night during a long print )
I have tried the Arc-Welder option, but while it was a considerable improvement, I still found better results when printing from the SD card.