Lightroom :: Affected By Size Of Catalogue?

Well to all those who simply could not accept that there was something wrong with Lightroom 4, take a look at Lightroom 5 beta. It simply ROCKETS along on my machine. The way it works is exactly how LR 4 should have worked. The fact Adobe have released 5 beta so quickly tells me they were simply generating revenue, as this release, and the new tools in it, is really what LR 4 should have been.
 
Anyway, I imported about 4,000 images and made it into a catalogue to test the beta.  The best tool is the healing brush, fantastic! However when I made a new catalog and imported all of it's 37,000 images, there was a significant slowdown. I remember a couple of years ago with v3.6 asking if catalog size affected performance and was assured it didn't. Well my simple test shows it does, although there could be a different reason.
 
As an aside, you can't use a v4 catalog they say so I had to make a new one. Presets etc work fine, but in my v4 catalog I have a lot of images flagged, and some in smart collections. Is there any easy way to replicate these?