Starting with the version 4.4 of our Windows VPN client app, we added support for the WinTun driver, an alternative to the classic Tap driver provided by OpenVPN.  

You can enable support for it in the Advanced tab > Use wintun driver if installed  

Wintun driver installation

The driver is not automatically installed, so you need to install it separately. There are 2 ways to do so:  

1. Download OpenVPN GUI from http://staging.openvpn.net/openvpn2/ and when you install it, check only the Wintun driver installation  
2. Run the wintun.bat install script from our software's "Tap" subfolder (e.g. C:\Program Files (x86)\VPN.AC Client\Tap)  

Advantages

Using the Wintun driver instead of classic Tap network adapter could give a speed boost with OpenVPN connections, over ~200Mbps which has always been the upper limit with the Tap driver. Use it only if your broadband speed is higher than 200 Mbps, else it wouldn't make a difference.  

Disadvantages

- Establishing a connection using the Wintun driver takes a longer time due to the delays/wait times when setting up the IP on the virtual interface. In our testing, the delay adds an extra ~10 seconds when establishing the connection.  
- The driver is still in experimental phase and it has bugs. For instance, we found that in some scenarios it's impossible to establish a connection unless the wintun virtual network adapter's name is changed.