ok, so these 'results' we're actually talking about were the first event in Sydney for the Australian season. Not everyone had their 161's at this stage, and most had just unwrapped them that morning.
My 160 is on a ship somewhere between Holland and Sydney and my 161 was in a truck somewhere between Sydney and my house. So I used the 159 with R19 S- that weekend. Sweeeeeeeeet fin. The 159 is still a sweet board. Sweet enough to win 6 out of 8 races by a bit, which is why the 161's were a little way behind in the results.
Have had a little while to sail the 161 this week. Remi is right on the money; an R19 is definitely what you want for this board. Makes the board considerably more stable and pointing incredibly high (and suprisingly with the size of this fin, its motoring downwind). So far that's all I've tried with as my fins haven't arrived back from Europe yet... but I'm confident in saying already this is the best starboard formula board I've sailed by far!