Large library lag & freezing

I am a music teacher and have a very large library with almost 50,000 songs. I just bought a new PC computer a few months ago specially built for me with a 500 GB SSD for start-up processes and 2+ TB standard hard drive (both internal) with plenty of RAM to boot. It currently runs on Windows 7. Once I got the computer, I installed iTunes.

At first it worked great. I have two disk drives and was able to rip two discs into iTunes simultaneously, while also being able to navigate and edit tags with no lag while playing tunes in the background. It worked like a dream.

After about a month it started to slow down. Now, it takes about 30 seconds just to delete a song from my library, during which iTunes freezes up. Ripping a single CD also freezes up iTunes until the process has finished, and download ripping speeds have slowed to a crawl. Editing tags is an exercise in patience as I have to wait 20- 30 seconds for it to save the track tag. Any thoughts or suggestions?