Virtualbox is working very slowly

[vboxUser]

After an update from Virtualbox 4.3.14 to 4.3.16 Virtualbox started to work very slowly. I'm using Windows 7 Professional 64-bit as my host system. For example if I start a guest VM, the update of the guest's window on the host is occuring very slowly; if I move the mouse pointer inside the guest VM it's not a "fluent motion" anymore but the mouse pointer is only redrawn after I stop moving the mouse. It hasn't been like this for Virtualbox 4.3.14 or any other earlier Virtualbox version.

I will attach a VBox.log for a sample testrun with Knoppix 7.2.0 CD as a guest system. I noticed that there is also a file called VBoxStartup.log, which hasn't been created before the update to 4.3.16 . This file is very large for the above testrun (over 300MB). Is there any reason for this file's existence and why it is so large? Maybe the slowdown occurs due to excessive logging of the guest VM's behaviour. If this is the reason then how can I disable this? I won't attach the VBoxStartup.log - file, because it's so large unless you want me to upload it.

Thanks.

[vboxUser]

testrun with KNOPPIX_V7.2.0CD-2013-06-16-DE.iso as guest's OS

[aeichner]

Please reopen if still relevant with a recent VirtualBox release.