I have heard the rumours and have also read some of the comments by dissatisfied parents prior to deletion - some clearly feel very let down by the Head and the GB.
Bear in mind that finding, appointing and inducting a new Head is generally quite a lengthy process (especially now as it will be done under a microscope) and any required change also takes time. An Acting Head generally keeps the wheels in motion, rather than implementing change/new policy. Any uncertainty or conflict at the top can also cause a flurry of staff resignations, further disrupting learning.
There is a popular view that the King's VAT pledge is not sustainable, especially if they continue to lose pupils, so parents may get a shock down the line - pure speculation of course.
The PR machine at King's has been extremely active over the last four years, but some information reportedly did not stand up under scrutiny, so be sure to fact check anything important to your decision making.
RGS does have an amazing Head with a wonderful, calm leadership style and I think the school is currently outperforming both King's and Bromsgrove. If the numbers continue to increase as they have been though, there could soon be complaints from parents at RGS because there is definitely a physical limit to their capacity, and no obvious investment in new facilities.
Hope that helps.