[Savage GT]

Generally (at least most later models) SCX will take Slot.it /NSR tyres. Nascars are an exception I think.
My home track Corvette GT, Merc GT3, Toledo and RS01 have Slot.it fitment urethanes.
A bit of weight as close to the guide as you can get, and possibly thinner (ie NSR 0.2mm) braid should sort the fronts, not sure if they are independent fronts on the Seats, but they can be quite good, but easily swapped (straight clip out of independent and clip in of suitable bushings) for a solid front axle if required.
The RK motors are perfect for home tracks