I just upgraded to Gigabit last month. Previously had 100 Mbps, no real difference except for the speed tests.
Not really worth it, but I'm paying ±28 EUR/month so no regrets.
Kind of. Current version has 3 modes.
Regular browser, Mini mode (which sends pre-rendered web pages back to the phone) and Turbo mode which compresses images and videos.
Using Turbo mode for now, best of both worlds - data savings and compatability with all websites.