Lag / performance drop

I have an existing world that I take through snapshots (with backups!). In this one, I've been building extensively in the End.

This snapshot has significantly decreased general performance. To try to combat this, I've tried:

• Reducing the render distance to 5 chunks
• Reduced particles to minimal
• Changed graphics to Fast

The two things I didn't mess with are VBOs and VSync (off and on, respectively, as I was also getting some screen tearing on the last stable release).

None of this affected performance positively. Any ideas?