I have Lancer 2007 1.6 GV manual transmission 85000 km on the odo (actual mileage). Here is my experience and answers to your questions ;-
.. The factory fitted cng is the best experience i've ever had.. pick with economy .. 150km/cylinder in local without ac everytime .. with ac it is 130km ..
.. When i got this car in last september its engine was never washed since 2007 .. i had to scrub every bit of dirt from it and now i get it washed on pressure with a shopper and piece of cloth on coils and few sensors around it .. i get it washed atleast once or twice a month (from no specified service station, it seems every service station staff knows how to service an engine with senors and EFI)and no problems so far
Engine bay pic after my first wash .. and it looks like this every time i return from service station
.. the factory fitted kit is tomaseto and i've heard that they (local mitsubishi people) made some special jig to emulate the EFI unit as without it the problem of starting and knocking was there. There are mechanics, who are fitting kits in lancer and these work as good as the factory fitted ones
.. on petrol i'm not sure but i guess it will it not give above 10 or 11 kmpl in local with ac ..