Lion vs. Mavericks: Which is best?

So I picked up a clean used Pro 3,1 off Craigslist this past weekend. Since then I've switched a few parts around from my old Pro and booted up using my main SSD drive. Currently, I'm running Lion (10.7.5) on my newer machine and I'm considering upgrading to Mavericks, due to the higher application compatibility. I really just want to prepare my Pro for some software updates down the line.

• Can anyone here tell if there are any performance differences between Lion and Mavericks (speed, stability, function)?
• I've heard that Mavericks was a disaster until the 10.9.2 update and improved upon by the 10.9.5 update; is this true?
• Where can I find the download link for Mavericks?
• Is there an OSX compatible app to erase the free space on an old boot HDD?

I am NOT willing to upgrade past Mavericks at the moment. Yosemite and El Capitan are too resource hungry for my taste and I dislike the new GUI. If I'm wrong about this, correct me.

Specs:

Mac Pro 3,1

OS X 10.7.5 Lion

Dual Intel Xeon E5462 @ 2.80 Ghz

16 GB DDR2 800 RAM

Sapphire Radeon 5770