Making this topic so people wont run into the exact same issues @Niran and I experienced. Hopefully this will save people a lot of mucking around.
The GV/GR fuel hanger seems to be a significantly restrictive part of the fuel system on late model STI's (MY08 - MY14). Because of this restriction it causes fuel pumps to get hot, cavitate, and eventually fail, causing big issues down the line. The part of the stock hanger which is returning fuel simply cannot flow enough fuel out of it to keep pace with the bypassed amount from regulator. What happens next is rather than the Return line being un-pressurized, it starts building pressure, which affects the performance of the regulator which in turn causes flow/pressure issues down the feed line, which then causes the fuel pump to cavitate. Cavitation link for reference if you don't know what it is. The Solution
This issue can be resolved by using a surge tank setup, or by replacing the fuel hanger with an aftermarket alternative. Radium Engineering hangers have been proven to resolve the issue, as well as the Process West surge tank option. The reason why going to a surge tank solves this issue is because you also change from a high pressure fuel pump, to a low pressure high flow pump which just dumps into the Surge tank. Additional Info
This may also apply to a select legacy GT's between MY05 and MY07. Someone to confirm, perhaps @Andy_Mac may know, but I believe they use the same hanger.
Please note that this discussion is aimed more towards people chasing big power (300kw +) If you are doing simple bolt-on's this may not apply to you so don't worry!
Solution A: Aftermarket Fuel Hanger
The below is for a Radium Fuel Pump Hanger. (20-0380-00, 20-0382-00, 20-0383-00) It is recommended to purchase the plumbing kit for this too.
Solution B: Surge Tank
Process West Anti-Surge Fuel System - https://processwest.com.au/surgetank-08-14
Solution C: Hack Job
Nobody we're aware of has tried this yet, if someone does can you take pictures and post up step by step instructions and ill add it in here.
Contributors: @Dairusire @Andy_Mac