I believe most people don't understand what avast! Script Blocker really does (it doesn't really have much to do with Excel, Word, etc. - only with IE). In any case, since the introduction of WebShield it became quite an obsolete feature, as the Web Shield will detect mostly everything the Script Blocker would, and more.
I must say I'm not aware of any scan speed improvements in progress (where did you read that, Mike?). I would say, however, that using the "Thorough scan" is overkill in most cases. The Thorough scan checks the whole files and all the files - that's why it takes so long (other AVs may not even have that possibility, I don't know). Using the "Standard scan", possibly with archives enabled, should be just fine. If you really want the thorough scan, don't be surprised it's slow.