Differences between METIS 4.0.1 and 5.1.0


I've been happily using METIS 4.0.1 for a while, but recently I switched to 5.1.0 for better 64-bit support.
However, on smaller graphs, which shouldn't have any issue regarding 32 or 64-bit stuff, I now get worse partitiongs (data clusterings in my case) than I used to get. Which parameters should I specify to gpmetis in 5.1.0 in order to get the same behavior I had with pmetis in 4.0.1?