^^^^^^^^^^^
Keep the original engine and upgrade so a swop back is available.
Basically your options are dependant on what your aims are...
a) keeping originality
b) increasing performance
The CVH , as Arwyn said, only allows relatively small power increases. Getting more is ££££££ as major mods are needed. That is the basic conundrum with any engine.
Bear in mind that bigger power can also lead to other upgrades for brakes/ suspension etc to handle the power safely. Don’t forget the insurance/ MOT/DVLA V5 changes too.
