What sails do you have up? Reefed main? What sized jib?
Are you beating, or just trying to hold that angle on one tack until whenever?
"Generally speaking" 25 degrees will have both sails inverted along the luff, and with a jib you'll risk getting caught aback if you head up too far. Also, you'll beat up your sailcloth a lot with all that luffing. But the sails will dampen the roll, and help your engine along a little.
45 degrees will keep your sails "asleep", dampen the roll more, and make her a little easier to steer. Probably more comfortable depending on your bow geometry and the particular boat design. But more real estate to cover if you're beating.
And this doesn't answer which speed thru water is going to get you to ride the best, again that's design, and wave-period dependent.
Oh, and as Faster said, you have to be careful that your cooling water intake, and prop, remain submerged. Otherwise, just bear off and sail her. And be careful, if your fuel tank's like most, there's some gunk and junk at the bottom, and motoring in a real rough sea can shake it up into the fuel line, and thence to your engine/filters/injectors/carb. Now you don't have an engine, and it's too lumpy out to fix it safely.
Last edited by nolatom; 04-20-2010 at 05:48 PM.