Download the release notes and carefully follow the directions. https://www.borisfx.com/download_files/BCC4FCP5.1%20patch.pdf
Most of the fix deals with deleting the FCP ObjectCache and Profs Cache. The script Walter refers to pertains to problems between BCC4 and Calligraphy on Intel Macs. Since your running a Power PC it probably doesn’t apply.
By the way I’ve found that you may have to delete the cache files on more than one occasion.
You have to purchase the entire bundle which is called Final Cut Studio 2. You can’t purchase the applications separately. This started with Final Cut Pro 5 I believe.
I’ve used Camtasia and it works quite well. They have a 30-day trial with no maximum capture time or watermark. At $299 it’s pricey compared to Snapz ProX 2 at $69.
For PC here is an inexpensive option, but I haven’t tried it https://www.deskshare.com/msr_pricing.aspx
It won’t hurt to defrag, but here’s what Apple has to say about it: https://docs.info.apple.com/article.html?artnum=25668
Aside from turning off “show waveforms” I really don’t know what could be causing your slow down. I’ve always heard that you should reserve 25% free space.
If you don’t have too many camera starts and stops you could mark in five seconds after each TC break and batch capture. That is if you can afford to loose the material. Otherwise Jerry’s suggestion to dub the tape with new timcode would be a good option. The downside is that the TC on your two tapes won’t match. You can always force the one of the captured tape’s TC to match using the Modify Time Code function in FCP. It might be tricky to find a visual or aural reference to sync the two tapes. Also if you loose your media you won’t be able to recapture the media with modified TC it won’t reference the original tape.