Wren Wiki help
When NOT using ASIO, in the device selector (main menu: setup/Audio devices ) use a buffer size like 2048. You can set a buffer size of zero, in which case the PortAudio DLL will decide on a buffer size.
When using ASIO the buffer size setting is ignored, and the size recommended by the ASIO driver is being used instead. So for ASIO you will need to set the buffer size from the ASIO control panel (and should set the buffer size in Wren to 0).
For the 32 bit version only there may be a bug in one of the modules causing it to produce denormal values, which will considerably slow down the DSP calculations (as shown in the DSP usage indicator). There is a diagnostic tool to find out about this, in the Debug Screen F5 you can turn on automatic denormal searching. Any modules getting or producing denormals will then be highlighted in the editor. Please report any such issues along along with the patch causing the problems. This can not be an issue for the 64 bit version.
Your patch may be too complex, have a look at the CPU percentage next to the module selector, at around 80% things can become critical, enlarging the buffer size may help, lowering the Sample rate and/or enlarging the Control decimation in the Settings Screen F3 may help.
The 64 bit version performs way better than the 32 bit version, so use that one if possible.