Efficiency of an IR emitter should not be a major consideration in this selection, nor should it play much of a role in any application. Generally speaking, electric emitters will be more efficient than gas emitters. And the radiant efficiency of the emitter is not critical, at least when compared to more significant factors, such as wavelength and response. These two factors play big roles in emitter selection, since they can most affect whether the heat delivered to the product or coating is reflected, absorbed or transmitted through the coating or substrate, and because of how quickly the intensity of the radiant energy can be adjusted, especially when staging and zone control is required.
All emitters can be adjusted for wavelength by changing their operating temperatures. However, not all emitters are designed to attain the complete spectrum of long, medium and short wavelengths. In your evaluation process for choosing an IR booster for your gas oven, you will want to choose the wavelength (as indicated by the temperature of the emitter source) that is best absorbed (or least reflected or transmitted) for your product.