Obviously, the more power you're sinking into the trans, the more useful any form of case reinforcement becomes. However, I think any time you can upgrade the hardware that holds everything together and find a way hold to bearings in place more rigidly, it's going to have a positive affect on transmission longevity and reliability. There is not much aluminum holding things together and the 5mt design was obviously not originally intended for this kind of punishment (for the reasons I highlighted in the picture on my first post). The 5mt as a whole is not engineered with a lot of headroom for increases in power, I think even the most seasoned subie gearbox gurus would agree there.
Go to your local junkyard and find an old manual subie... You will find that the transmission in a sub-100 hp 20 year old Subaru is not very different from what's bolted behind the engine of a heavier and wildly more powerful WRX.
Will the reinforcement be an end-all fix for th Subaru 5mt? I seriously doubt it. That's why I'm trying to keep it pretty affordable. When there are really clear shortcomings in the case design, it seems silly not to put $100 into stregnthening the foundation of your transmission... And for folks running above stock power and/or expensive aftermarket gears, it seems like a no brainer to me.
Time will tell. xdrian is pushing good power and the diff brace will definitely be put through its paces there. Once the main reinforcement is done, a pre-production example will be sent off to Dylan at DS1 to get his impression as well. I'd like to try to find a couple of applications where these parts are punished relentlessly to see how they hold up... I was thinking of making a test fixture to measure deflection at different parts of the case with and without the reinforcements in place... But first thing's first: I want to get the basic design along with fit and finish worked out before moving on to heavy data gathering. Besides, there's no better proof of concept than putting a part in its intended environment and seeing how it performs under real-world conditions. If xdrian's case hold up with the brace installed, it doesn't prove much right off the bat, but it would provide compelling evidence to go into further testing.