New iPhoto Very Slow on Mavericks

Question

Basic specs:
- iMac (Late 2011, Dual Thunderbolt)
- 24GB RAM
- iPhoto Library at 800GB, 110K photos, ~300 albums over 10 years)
- New photos shot with Canon 6D (RAW + JPEG). Ave file size for RAW ~16MB, JPEG 4MB.
Symptoms:
- iPhoto 11 worked incredibly well.  Would shoot a few hundred shots, import, then run through and tag / flag
- Upgraded to Mavericks.  No issues with old iPhoto.
- New iPhoto installed, now rendering of iPhoto thumbnails takes 30-60s to resolve when opening album
- Arrow keying through photos in album takes 20-30 seconds per photo.  Impossibly slow.
Any clues on what might be happening? 

Answer 1

Just posting to close this out.  I had left iPhoto up and running on my machine all day (12+ hours).
Interesting - it's now very fast. The disk access has stopped, and I can browse / edit / tag photos extremely quickly.
The only two things I did:
- Last night I opened my iPhoto Library in Aperture, browsed an album to verify the problem was NOT in Aperture / the library.
- Reopened in iPhoto, left it open
My best guesses now:
- There is some background task (updating every thumbnail, updating facial tagging/guessing) that was running through 800GB of photos in the background.  Once complete, the app is responsive.
- iPhoto knows when you complain about it on apple.com and that puts it on good behavior.
Not sure, but glad it's working again.
Adam