Hi guys,
Thanks for the replies. I managed to sort it applying the config above and uncommenting config_hdmi_boost=4 as well to boost power. Got it running consistently now!
I did want to use an external USB stick to host the ROMs, but the power goes crazy if I plug anything else in... So I'm going to copy the files to the SSD, or use a USB drive with an independent power supply.
Once again, thanks for your quick replies!
Matt.