You can never have the best of both worlds because there is always a compromise. I've had 2 cars on duel fuel.
My first gas car was an old V8 VH Commodore (carby) and it was tuned to suit gas and as a result pinged (knocked) when on petrol because the timing was too advanced.
My new car is a VS SS Commodore.
It doesn't run as well on gas but that's to be expected because it's designed to run on petrol.
It idles high on petrol now (about 1200rpm) to compensate for when it runs on gas (about 600rpm). It can't be the same for both.
Also it loses heaps of power. Had it dyno'd at the RE customs dyno day and it made 130rwkw on petrol and 80rwkw on gas.
I'm really happy with it though because it's cheap to run and is great for towing and if I need more power I just press the petrol button.
If you want a good gas system it would have to be dedicated gas or something like gas research. No good if you run out of gas though. Can't just get a jerry can of gas to get going again!