What is considered heavy by your standards? Some list the weight, some don't.

The wheels in post #17 are made of "aircraft aluminum alloy – the strongest, lightest, highest quality aluminum available" according to the listing.

The previous 19" set I had was 13kg (26lbs?) on the rear. That didn't work at all.... cast alloy wheels in the 10.5 config. NO GO

The one that I have now a little better, 9.6kg and considered ultralight by our industry professional standard, but still... feeling sluggish dunno. Definitely not the same as those SUPER light and cheap 17" cast wheels that came original with the car.

Mind you mine is a the fastest Boxster of all, the mighty TWO point FIVE liters! Might be less noticeable with the 3.2L engine

That would be a wheel that cost min $2,000 each if indeed forged, or CNC out of aluminum. Don't know man, not a wheel professional here. Try your luck!

I'll keep the weight in mind, not only for gas mileage, but also for rotational weight at the corners.

My summer tires were 255/40/17 so the tire size diameter size was 636mm.

I'm wanting to go to 275/30R19 so the tire size diameter size is 648mm.

This will lower the gear ratio, which could cause the feeling of sluggishness off the line. I did imagine the width of the tire would hurt gas mileage, but might not be as bad with the lower gearing ratio?