I have driven both back to back, on taking my new car on a test drive and when I picked it up. All I noticed was the fuel guage going down quicker on the new one 
Scientific proof!
Meant to reply to this thread first thing this morning but had just finished a night shift and was too tired.
Rewind back to 2013/4 and there was a lot of wondering why the pan roof and 19’s couldn't be be specced in the UK together.
Conspiracy theories were that the harder ride would crack the glass due to less shell rigidity but eventually VW said it would cause the car to slip into a higher emissions bracket.
Over the lifetime of the model the tax rules changed and with the facelift refresh the two options could be specced together.
Yeah, there might be a slight weight distribution penalty but in real world driving not one you’d likely notice as others have said. Tyre pressure variations would be far more noticeable.
Maybe a slight reduction in torsional rigidity with it open?
On a tall, narrow and short car like an up! GTI (with its more basic and compromised suspension) it would probably be noticeable if you drove two cars back to back with and without.
On a hefty Golf... nah!
