I know that Metoprolol overdose feeling; dragging, dull, heavy chest pain. At one point, I was up to 200mg. for a month, so I can relate to what you're feeling. I think you have to weigh the significant risks involving ablation and the location of your accessory pathway vs. drug therapy and living with your condition. How often do your events occur? Are you able to convert them yourself by some means; Valsalva, etc.? At 30 years old, time is on your side. Perhaps a new technique in the next decade will make your particular situation less risky.
Verapamil is a serious, Class IV anti arrhythmic that is indicated for SVT. But you're not out of drug options, and maybe a different one will work you. But As you know, they too carry some risk as well. Hopefully, some food for thought.
I'm not sure how long you've been on the Verapamil. I was given Diltiazem, also a CCB, for my heart because I couldn't take Verapamil. When I started the Diltiazem I had a non-stop pounding headache for 2 weeks. It gradually eased off and my body adapted to the med. It probably has something to do with the way the medication works to relax the blood vessels a bit.
If you've been on Verapamil for awhile and still have the headaches, tom is right: there are still other options for you. Strangely enough I did not get headaches with Verapamil, just chest pain, shortness of breath and pain/weakness in my legs. The Dilitiazem was much better for me.