I followed your advice and exported all of my hands from PT2 into HH files. I then used PT3 to import. At first PT3 imported very fast at 300h/s, but after a few hours it slowed to a crawl at 6h/s. I have about 2million hands in my database.
Sometime during importing from these HH's, PT3 even crashed. I think everytime I've tried to import for longer than 1-2 hours, windows pops up with an error msg saying an error occurred while running PT3. It was the same msg as I got when I tried to convert from PT2 into PT3 directly. PT3 can run while the error msg pops up as long as I don't click the send or no-send buttons on the error window. The only problem is that the import process takes way too long.