The work you did probably is great and do I think its above your average developer. Somewhere in the the top 10%. Though how you conducted yourself in the face of management was down right petty/folly.
Yes you did the best job in the world. You improved the performance of the serves by % and it did make management of those server's easier. Though you need to think about what you've done in the eyes of management.
Firstly you've modified the server's without permission. You've run tests out-side of work hours that could of impacted the business bottom line. For all I know (its up for debate) but your senior managers had more pressing issues on the table, and having a young code money running around outside office hours is the LAST thing they want to hear.
`It's not a simple as you may think it is.`
Some of the things that come to mind, and honestly I would of pulled you into a office to explain yourself if you're on my team.
1) Did you document all the changes you've made to the server
2) Did you back-up or store any sensitive information off-site during out of office hours
3) Did you modify critical system files that could cause another dependent system to fail
4) What ETA/Service level agreements if any did you break when bringing down the server for maintenance?
5) Did we lose any Security Certification with you modifying the server or changing any of the certificates on the server?
We're software developer, and yes when we see problem's we want to fix it to our best of our ability. Though when you're in a Business there are many thing you may not be aware of. In this situation I would honestly say you're lucky to keep your job! I hope you take it into consideration next time you want to go out-side of your duties.
I don't want to come down harsh on you, but there are times when you see a bad situation and there is nothing you can do about it. You notify the people who're higher than you of the situation and the dangers. It's then up to them to make the decision. After they've made the decision that is it. If the server blows up during the weekend, and they want you to come in and fix it (even when its there fuckup) you just take your hourly rate and x10. So if your hourly rate is $50hr and the server blows up, then your new rate is going to be $500 per hour to come in during the weekend to fix the mess.