I almost never sail with only a jib. If I sail with only one sail it's the main. However, I would expect to lose at least 10˚ - 15˚ of pointing ability with only a jib; particularly as the wind pipes up.
A light, little boat like that is going to have a tough time of it to windward in a stiff breeze. Current and waves are going to make it that much tougher. However, with a tightly sheeted working jib and a helmsman who is really paying attention, you should be able to make some progress in anything shy of 25 or 30 kts, or so. The key is to not be too over-canvased (reef early, reef often), and "work" the waves and the puffs as much as possible, scratching out every bit of windward performance you can.
Thanks for that. I had 15 to 23 knots and wasn't paying attention at all until leg 3 and the main is very tired.
Next time I'll try to get better numbers.