So I imported my PT3 DB into PT4. All went smoothly, except some old pre-2010 PartyPoker hands were imported w/o 6max tag, because there was no indication of that in the HH. So I adjusted the sessions manually to 6max. (Btw, is it possible to add some more filters to the "Adjust Stakes" function? It was a pain in the ass to search for all the sessions manually. I know you can sort by klicking a column heading. I have more like site + stakes + timeframe in mind.)
After that I went on to look at some hands in the replayer and was surprised to see that were shown at a fullring table rather than on a 6max one, the way it was in PT3.