It think it has a lot to do with where the wind is coming from. If you have a cross-onshore, as is common here in hong kong, with the wind coming in from about 10:30-11:00 when looking at the water, naturally reaching towards the beach is faster than reaching away as the board hits chop less frequently due to the way the waves are moving.
In addition, far out in the bay there's some ocean swell, and if you're already blasting at say 25knts, riding down one of these while coming towards the bay can add 1-2knots in your speed. This doesn't happen when riding out away from the beach as you're working against swell.
I feel much more comfortable going upwind out to sea, so that is usually port tack, and I have lots of trouble keeping upwind on starboard. I think that is due to the waves/current. On the GPS tracks, my upwind angle (and this is usually none planing, due to the wind in HK being mainly gusts then 5 min lulls) is about 30degrees worse on starboard tack.
Also, I usually feel my obliques working super hard when going upwind on starboard. Upwind on port feels so much more comfortable, plus I can get some good jumps on port.
Just got my RAM fixed so it'll be interesting to see how much faster I can go with that over the current sail I've been using.
JP Super-X 106l, North F8 Ram: 5.8m,