Stabilizers defective or crossbars?

Hello girls and boys! In January I got a Opel Omega 2.0 16V (purchased, because last car (fiesta) total damage) with approx. 95000 km Built. 8/98 with bla and text as equipment etc… I am quite happy with the car. But one thing is not for me: At a speed of approx. 70-90km/h the steering wheel wobbles as if one could think the car falls apart. From approx. 90km/h the wobble then disappears again and comes back only at approx. 140km/h and then disappears I had new winter tires put on new rims, and the wobble is not gone… I asked Jeztz what could be all this, and I got a lot of different answers: first it is the axles, then the stabis and then the crossbars and and and and… Now I thought, people from the forum know that! I hope!! Oh yes, and what else: is it normal when I go on the gas and the omega (e.g. on the aut) And that: If the engine is cold, that then a whole while sounds like a mixer with problems? That was it again from me, I would be glad for every help greeting mike 69