Re: Ride comfort
What upsizing means:
(1) to ride comfort - on low profile (and wider) tyres, you will lose ride comfort but gain surface traction (assuming better tyres such as PS2 or RE11) vis a vis your stock RFTs. As with all handling enhancing mods (coilovers, ARBs, struts, control arms, bushings, cambers, wheels, tyres), you risk comfort in exchange for better handling.
(2) to acceleration response and fuel consumption - a myth. It all depend on the weight of aftermarket wheels and tyres. From 17" set up to 19", the rolling radius (wheel's radius plus 2 times tyre's (aspect ratio times width)) increases slightly. But the weight of the aftermarket wheels plus aftermarket tyres might be much more lighter than stock wheels plus RFTs. This applies to many lightweight forged wheels.
The most important aspect is the weight distribution of the wheels/tyres combined weight - the RFT means greater centrifugal force is required to move the wheels (heavier outer weight) as well as braking . Try to visualise heavier weight on stock + (heavier) RFT set up, versus larger but light aftermarket wheels and lighter tyres. Similar rolling diameters, but which set up takes require more energy to spin?