On my other post where I said to double the BTU's, that's to get the starting watts you will need. So with an 8,000BTU AC you will need roughly 1,600 watts of power for start up.
On average, typical single-phase soft-start capacitors reduce startup surge by 20-40 %.
Some Marine Dometics have a built in soft start, that reduces start up surge by 60%.
I think the Coleman Polar Cub A/C has soft start capacitor kits from the factory.
Some people have reported that their able to start, and run a 13,500 BTU with soft start, with a Honda 2000, but I really think this depends on the brand/type of A/C, and altitude.