Class E airspace, can ATC really give an exemption to a statutory speed limit
In class E? I would not think so. Even if ATC technically could, not too many ATC's would accept responsibility for increasing the risk [higher closing speeds] to pilots [the unkown VFR and/or IFR] who are left reliant on seeing [and avoiding] each other.
In terminal area [where climb and descent is part of the conflict exposure] E, nobody knows with any certainty, the track or altitude intentions of a large proportion of the conflict scenarios i.e. the VFR component. In D or higher categories they do.