Personally I say don't waste your money on a 20v as they're very underpowered ($$ per horsepower). If you must persist with an A-series engine then the 4AGZE is the only choice. If you're wanting to stay atmo then you're probably just as well going for the 16v 4AGE - no they're not as powerful as the 20v but they're about 3/4 the performance and 1/4 of the price.
As for the K series engine I can't help you, but the thing is never going to be fast if it's got an engine like that in it.