If I had a decent scale i would weigh my panther maxx slicks, but I doubt they would be lighter than the phaltlines any way. You could use 1/8 buggy wheels, then your lightweight onroad tire selection would be pretty extensive. Or you could drill some 12mm hexes out to fit your 6mm axles and use jato wheels and anaconda tires.
For onroad use, smaller wheels and tires are better in almost every way, you just need to decide how important the monster truck look is for your maxx.