Definately go the ST165, you've got a a pretty good deal. Especially a very god engine!!!
Seriously though getting a ST162 and doing the the GT4 conversion is really not worth it compared to buying a ST165 straight out, trust me I was gonna do it, but I took a long hard think about it.
There are heaps of st162s on the road, but sh#it all st165s.
GO THE ST165!!!