you will be able to stick with the lpg mixer if you wanted, but would just have to run alot less hp, because getting towards the combustion conditions you are wanting to make high hp from high boost everything in the fuel mixes accross all cylinders and /ignition timing needs to be PERFECT.

i look foward to hearing what your lpg guy says, just ask him what he thinks the limit of the mixer is, you may find you will be happy with what it can produce,

High hp numbers can start to become a large pain in the ass tho, as it starts to stress all the rest of the components in the drive line, so you will find once you get the engine sorted there will just be something else which needs to be changed aswell to cope, and so on and so on,
plus with a road car with high hp it is really impractical like my car by the time you get into a higher gear like 3rd-4th to really let the power down you end up going so fast in such a short time its just rediculus, u end up with a track car really