Fresh off a bunch of F flights on both aircraft, couple of comments:
A380 showers, room for two?
Loads of room in the suite itself, although mind the underfloor heating - it does get quite hot!
Sufficient room in the actual shower for two, but one of you would need to be sat down on the inbuilt seat. I'm sure you could take up appropriate ahem 'positions'
A380 showers interruptions?
The shower girl is often used to perform other tasks on the aircraft. I had a recent flight ex:MAN with only 5 in the F cabin and only 1 (me) elected to use the shower. Whilst I was in there, both the shower attendant and a cabin attendant waited outside the suite and only moved once I had exited it.
The attendant did spend a lot of time putting together duty free purchase bags and then distributing them further back in the aircraft for a couple of hours during the flight.
I would guess it would be possible on a quieter flight like this for two people to quickly enter the suite whilst the cabin crew and suite attendant are busy elsewhere. Whether you would be met upon exiting the suite is always going to be a gamble......
A380 1F
Not sat in it recently, but it doesn't seem to me to be any different size wise from all other F seats.
777-300ER Seat 1A
Is not narrower than corresponding K seat - it' s no different to K. Sat in 1A twice in last week and the only annoying thing is the noise coming from the forward galley. The purser tends to base themselves on the 'A / C' side of the galley and I feel you tend to hear more phonecalls / instructions / walkpasts down this aisle rather than the 'F / K' side.
FWIW, when I get the choice, I go for 2K on both aircraft.