Thanks for the reply.
what will this effect?
Sketches built for that board will run correctly at 8 MHz.
Everything will still work? The only info I could find relating to this was from several versions ago, and apparently some things like PWM could stop functioning properly. Have all the functions been made CPU speed-independent now, then? Just want to make sure, as this chip has a range of tasks to do, from servo control to serial comms.
Do I also have to fiddle with the bootloader somehow?
Possibly. To upload at 115200 baud, you will need to install a bootloader built to run at 8 MHz. You may be able to halve the baud rate and leave the existing bootloader.
I thought this might be the case. I suppose that changing the mega2560.upload.speed parameter will change the upload speed, but as for modifying the bootloader I've no idea where to even start. If I want to use the Arduino bootloader, I can just modify that, right? I found the .hex files, but couldn't make head nor tail of them (What with them being a long list of hex numbers...).
Thanks for the help so far...
Tom