I would also highly recommend considering optical image stabilization in your lens selection. It will make a bigger difference than lens quality or maximum focal length in the quality of your images unless you are using a tripod. On a 1.5 crop body, 200mm is the equivalent of 300mm on a full frame, and that is a fairly long zoom. 300 would be the equivalent of 450 which is extremely long (like able to make out people with a fair level of detail almost a mile away if they have sufficient resolution).
As far as a comparison to a 10x zoom, 10x is a useless measure. Without a base focal length, it could be a wide angle lens with almost no range (say 1.5mm to 15mm) and even with a major crop factor, it would still only be like an 8mm to 75mm lens on a 35mm which is wide angle to standard zoom.
The bigger concern I see with your situation is losing the 55-70mm range. That's a fairly key range that is equivalent to the 75 to 105mm range in 35mm lenses. That range is the prime head and shoulders portrait range. Perhaps you don't have a need for that range with what you shoot, but I'd play around a bit with seeing what you'd be losing if you couldn't cover that range.
Overall I think you'd be better served with a 55-200 that has VR though if the only options are either add VR to your current lens or extend your focal length range and still not have VR. It simply has more practical value in resolving a telephoto image. (sharp and less zoom is better than blurry and more zoom.)