I've flown on 772s and 773s of Cathay, Thai, Singapore AL
, Korean AL
and and 772s of BA
. Never flown on a US airline's 777, though. Found them to be a great experience, almost always.
The takeoff roll will be faster and more enjoyable if the a/cft is not entirely full. I've had some 70% occupancy-takeoffs on the 772 and it feels great. The engines generate over 90,000 lbs. of thrust each so if you haven't experienced the accelleration of the 777 yet, you will immediately realize the difference between this phenomenal aircraft and something like the A340-300 or A330, or even a 747-400 for that matter. The speed of the aircraft inflight depends on many factors like allocated flight level, wind speed/direction etc. so "ideal conditions" for max. cruise speed will depend entirely on conditions prevailing on the day of your flight, and also, your luck.
If you are in "Y" class, try and get yourself a seat forward of the wings, if possible. Different airlines have different seat numbers but the first row in Economy is normally row 12 on MH
/SQ/CX and you should ask for a "A", "C" or "J" or "K" seat (window or aisle). Don't make the mistake of taking one of the middle seats (D-E-F-G-H). 29J or K are good seats, just aft (behind) the wing and exit door, so you should get good legroom and a good view if you are on 29K. Most airline websites offer seat map views - go to the UAL website and check if it's available and then you can select your seat and ask your travel agent to block the seat for you.
Have a great flight on the 777 !!!