@finbar – I picked mine up for a smidge over 30squids.
6.6.0 firmware is down-gradable on some PSPs (CHECK YOUR MOTHERBOARD USING pspident as per videos below) to 6.2.0 which can be made into a permanent custom firmware (you could have it as a “light” custom firmware, which would need to reloaded through a simple onscreen app each time to shut down the device.)
This tutorial is very good, as he explains exactly which motherboards can be used, and the over the two videos how to get the firmwares onto the device.
[video]https://youtu.be/TB9M8qH1eTU[/video]
[video]https://youtu.be/7dnXr8Z2UIM[/video]
There is also this huge wiki http://wololo.net/cfw4dummies/
As for games – which platform was Silkworm/SWIV on? I have fond memories of that! And NARC was awesome as well. I loved sabbateur on the Speccy.