Today liquidzigong of the Chinese board A9VG.com (linked above) has released PSP Custom Firmware 5.03 and 5.50 Prometheus, which enables recently released PSP Firmware 6.20 games such as Metal Gear Solid: Peace Walker and Kingdom Hearts: Birth By Sleep to run without patching required.
Download: http://bbs.a9vg.com/upfile/get/00b387fa4e41644d0cc394bab0d97f28/5.03_Prometheus.rar / http://bbs.a9vg.com/upfile/get/7f57c58eba847971cd2e0d21474b0a97/5.50_Prometheus.rar [Right-Click, Save As]
For those who missed it, an updated PRXDecrypter and PSPCipher by hrimfaxi reportedly allows the same, and the latest PSARDump by coyotebean also now supports Sony's PSPgo console.
The 5.03 Prometheus PSP CFW above is intended for PSP 2000 - TA088v3 and PSP 3000 users, with more details on the release available http://bbs.a9vg.com/read.php?tid=1505568.
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