Dark_AleX, co-creator of numerous downgraders and the 2.71 Homebrew Enabler and DevHook mods, has just released a major custom firmware mod for firmware 2.71: 2.71 Special Edition! According to Dark_AleX, the firmware allows you to take advantage of the benefits of firmwares 1.50 and 2.71 at the same time:

"Homebrew can be run on both kernels, the 1.50 one and the 2.71 one, letting almost all current homebrew work on the 1.50 kernel, and 2.71 homebrew compatible with HEN C in the 2.71 kernel.

Note: the installer writes to FLASH0. I am not responsible for any damage that may happen, since this software is provided free and without warranty. TA-082 users cannot use this because a 1.50 bootstrap is needed to boot the patched system.

At the moment, there is only an installer for 1.50, although it could be easily ported to any firmware with kernel access such as 2.60 and 2.71, but at the moment I prefer not to do it to avoid TA-082 using it and bricking their PSPs.

Note that this package DOES NOT contain any illegal material. The user has to provide the 1.50 and 2.71 updater PBPs to legally generate the DXAR file used for the flashing."

Again, to re-emphasize what Dark_AleX said, do not attempt to use this on a TA-082 PSP, as it is guaranteed NOT to work.

Be absolutely sure to read the Readme.txt included for more specific information, including details about running homebrew in the different kernels, running DevHook, using the recovery mode, and more.

The recommended method for installing the custom firmware is as follows:
1. Unless you're already on 1.50, upgrade to 2.71.
2. Use the Dark_AleX Generic Downgrader to downgrade to 1.50.
3. Use the firmware dump helper program to make a 1.50 firmware dump.
4. Use the Generic Downgrader to flash 2.71 SE.

Update:
A couple of bugs have been discovered. First, setting your language to as Korean/Chinese is not possible. Second, if you want to update, Dark_AleX does not recommend running the official updater, as it will display an error. Instead, use Dark_AleX's generic downgrader to reinstall a normal firmware, then run the official updater.

Excellent work, Dark_AleX!

[Download - Firmware 2.71 Special Edition]
[Download - Dark_AleX Generic Downgrader]
[Source]