If the answer was simply:
Flat, then why do you think the racing boat pictures would show a boat heeled over? It's not nust a photo op. (This is usually upwind or possibly on a close reach.)
Do you think the racing boats aren't interested in speed? ;^)))
As you others may say -- It depends on the sail plan balance, the apparent wind, whether you're having to use the rudder to keep the boat in in line (that brakes the boat), the seaway, and other factors.
The simple answer I give is: "USUALLY" having the right sails up and not overpowering the boat (where the helm becomes difficult to control and requires over steering to stay on line) AND having a balanced helm that is pretty close to the center line of the boat is fastest. You can prove that wrong in some cases by futzing around and really overpowering the boat -- but absent that, balance is good.
Off wind, in wild seaways, there are some hairy sleigh rides that might be faster -- but for mortals in light air or without huge amounts of sail up, generally flatter is better OFF the wind (on deep reaches and with the wind well aft).
The boat above probably has it's helm pretty much in line with the boat's direction. The heel is just where it settles down. The boat will let you know when the rudder has be kicked more than a bit over to keep the boat from either rounding up or falling off. Some boats with bigger rudders can be "steady" but the helm is actually too far over because the boat is overpowered or pointing too high.
Another factor, which people neglect, especially when going upwind: Actual course-made-good. If you have a GPS, see if your heading matches your actual direction over ground (forgetting current). You can have the illusion of speed through the water -- but you're sliding the wrong direction.
Stay in the groove. :^)))
With your Catalina 310, from looking at its lines, I believe that you have a relatively large fore triangle compared to your main. In light air, you would generally want to have a larger genoa -- but that would get overpowered as the wind goes into the moderate to heavier ranges. If you are beating, you would tend to want to reduce down to a working jib (say a 100% of the fore triangle area relatively quickly. If you don't do that and have a 130% or larger genoa, then you'd quickly become overpowered, especially upwind in say 12 knots or greater beating. You might compensate by reefing the main; but you need to figure-out how to balance the helm.
Anyway, that's my
pointificating for the moment
)))
