I have never sewn on a Cowboy, but I can tell you from personal experience about the quiet, power, and customer service of the Cobra. All of my previous sewing had been done on an Artisan 3000, and I followed the advice of Pepper and others on this forum and Leather Pros and went with a Cobra 4. When I got mine, I experienced some problems which I attributed to lack of familiarity with the machine. I sewed some more and didn't improve much, so I called Steve. The first night, he spent over an hour with me on the phone, talking me through various operations on re-threading, tensioning, and lubrication of the machine. I didn't seem to be having much luck in the following days, and Steve called me back on a Saturday night to see how things were going. He spent another hour that Saturday working through various diagnostics.
I emailed hom a couple of days later and told him that I'd about decided that I was too old and set in my "hand sewing" ways and probably didn't have any business owning a high-tech machine! Steve called me on the phone that night and asked that I ship the machine head back to him in California, and that he would pay for the shipping!
I did, and I had the machine back within a week. Steve called to tell me that he had reset the timing and changed a part. This thing sews like nothing I've ever seen. It even makes me look like I know what I'm doing (and that ain't easy.) You won't do any better in terms of quality than with Cobra, and I'm betting that you'd be hard pressed to match the customer service anywhere.
Hope this addresses some of your questions.