I was not aware that it has become an academy school and I really don't know what actual difference that makes to the school itself - perhaps it is merely about how it is funded/managed?
OK, I have visited both these schools and I know a bit more about Ashby than I do about Wymondham in a personal level. The reason I asked about boarding and the age of your child is this:
Both are day schools and boarding, which means that the boarders tend to be very much in the minority - particularly at Ashby. As they get older (and into 6th form especially) the boarders can find it very difficult to integrate with the day pupils outside of school hours, at evenings and weekends as they have very little freedom and autonomy compared to the day pupils. They can go out independently, in theory, but not much to be honest, and they have to get permission in place from their parents in advance, so spontaneous trips out at weekends with friends who are not boarders is not terribly easy. As a result they are encouraged to do everything pretty much together. Some kids will love that, others will find it incredibly restrictive and depressing, especially if they are new to boarding and are already quite used to an element of freedom and independence at home.
Many pupils in both these schools go home every weekend, which can leave termly boarders at a loose end and they can get very bored and stir crazy. If that is a risk for your child I would say pick the school with the largest number of regular/termly boarders in your child's age group, which would probably be Wymondham.
Both are lovely schools with lovely grounds and lovely facilities - Ashby's boarding house is superb, but Wymondham has the edge on outdoor space. Ashby is very close to the small town centre, which can be a plus, or a frustration, depending on the nature of your child! It's a bit tough to have it on your doorstep if you are not allowed to walk into town unaccompanied. Whereas Wymondham is much more rural/remote, so there is less temptation to sneak off, but Norwich is closer to Wymondham than Leicester is to Ashby, iyswim. A teenager who wants wall to wall action might go nuts at Wymondham unless they throw themselves into every sport going, as there is literally nowhere to get to on foot.
The staff at the boarding house at Ashby are fab. Lots of the senior boarders are international, particularly Chinese. I know less about the inner workings of Wymondham, but although i think it is probably a more impressive school it felt slightly less homely to me. Having said that I would still consider sending my child to either school.