Well the key to getting the most out of modifications is the ECU, how easy is it to map.
The Coil Pack K11s were fantastic engines as standard, but really do not take well to being tampered with it really is a case of fitting Omex which is a long winded and expensive process.
The earlier K11s are far better from this point of view. Either using a piggy back ECU or better still having the Standard ECU mapped releases a lot more potential out of the engine. I know ed will do the standard ECU mapping for a figure of just over £300 (please check with him to confirm prices).
If you have the money to do it, I'd go with the coil pack engine, the CGA3 and go with Omex.
Otherwise go for a pre 2000 K11, and spend the extra money on head work and wild cams, along with an ECU re-map.
Just my 2pence worth. Above details may not be 100% accurate.