You could nest on the right groups with less elements but under some major groups and the right doesn't need to be that big anymore.
Just an idea

Regards,
Vinzenz
1,2,4,5,6 is fixed<eranif>21 evilissimo: I have downloaded the patch and tested it. It looks promising, some comments:
<eranif> 1) you forgot "MyLabel" in one of the static text
<eranif> 2) you should use WindowAttrMgr class to save and restore the dialog last size and position to load old values, add this call to the last line of the constructor of the dialog: WindowAttrManager::Load(this, wxT("OptionsDlgAttr"), NULL);
<eranif> to save them, add this call to the dtor: WindowAttrManager::Save(this, wxT("OptionsDlgAttr"), NULL);
<eranif> 3) You chnaged one of the wxFlexGridSizer from 3 columns to be 2 (in the General page)
<eranif> 4) items should keep their 5 pixels spacers between each other, otherwise, it looks bad on Mac
<eranif> you should keep the layout as it is now
<eranif> 5) since you are using separate page for each category, the wxStaticBoxSizer are redundant, please use wxBoxSizer instead
<eranif> 6) It would be nice to center the dialog buttons (ok, apply, cancel) to the middle (unlike I did it, were I aligned them to the right...)
<eranif> thats about it
well I tried to make it as much similar as it is now however I changed the layout of the FlexGridSizers to 2 columns because it looks better (at least if you have a smaller window.you should keep the layout as it is now