Try this:

1. edit a large file (my test was on 150K of syntax-highlighted source code)
2. convert it to HTML with the TOhtml Vim script: ^O:TOhtml
3. wait ... and wait ... and wait ... (I gave up after several minutes, and the file was still only 15% converted)

In Vim, the same test file took 45 seconds: long, but not unusably so.  I did all edits on Linux on a local drive (/tmp, which is a ramdisk).

While I was waiting, Cream would alternately blink back and forth between updating the "File" menu and updating the "Window" menu.  If we could defeat most or all Cream autocmds during this expensive operation, only re-enabling them (and triggering them) when we are all done, the performance could be greatly improved.