The XB-70 is from Virtavia. I wouldn't expect anything good from it, excepted a nice 3D model. There are some exceptions, but this brand has never been considered "serious" for the realism of the addons. I have their Apache, Kamov Ka-50 and their Albatros.
On all three aircrafts, the external and internal models are quite nice (at the time they got released), but the virtual cockpit has almost nothing clickable, excepted the systems you also find in the defaul Cessna (battery, lights, and that's all...). Ah, for the Albatros, it's even worse... if I remember correctly, you can't even make a simple cold&dark startup with that plane, because some very elementary commands are missing from the VC.
So, anyways, I would avoid that brand if you are looking for serious addons.
The good thing about Virtavia is that they bring to the FS world a very nice set of "exotic" planes that no other brand ever modelled. And they do this at reasonable prices too. But the realism is not their strength at all.
Concerning the other brand, which is GlowingHeat, I don't have any of their addons, but I have heard/read some positive feedback about them.
The B-58 has been presented on this forum and the feedback from the customers wasn't bad at all, if I remember correctly. Also, Rick is working on some amazing metal textures which are bringing the visual realism/beauty of this bird to an extreme level. It might be worth it to investigate about that one (perhaps a search on the forum will return some results ? )
The SR-71, I don't know much about it. I heard it was a "serious" addon but I believe the graphic level is showing its age. I would be interested to hear about the realism of this bird too, actually. I've been hesitating to buy it for quite a while...