I found this searching for Cosworth on the net. I found this portion that I think will help the 2.0 guys feel a little better about their engine and installing Cosworth parts on their engine. This is from Sports Compact Car "Cosworth 2004 Ford Focus." The 3rd sentance being most important and coming straight from Cosworth.
"Importantly, the Duratec engine architecture is shared with other global Ford products; you'll find the 2.3-liter in the Mazda3 and Mazda6. Most notably, a 2.0-liter Duratec powers the new Mazda MX-5. Ken Anderson of Cosworth tells us that with the Cosworth packages installed on the 2.0, it makes only 5 percent less horsepower than the Cosie-modified 2.3-liter. We like the sound of a 190-wheel-hp, normally aspirated Miata."