I think either option would be fine. Two big pendants is very in right now and yes, I think at 16'' by 13'' they would be big enough. I will add though that 16'' is tall and if you onl;y have 8 feet ceilings make sure you are okay with how that will look. I *loved, loved* a pendant that was 18'' long and it was just TOO BIG for my 8' ceilings. If you like the look of two big lights, go for it. Does the rest of your kitchen look really symmetrical? If so, then maybe you do two to keep that vibe OR maybe your do three to shake it up a bit and keep it from getting visual stale and predictable. Hang balloons, paper plates or cardboard cutouts to get a sense of how each would look - although, if you are like me, you had to make the decision before the island was even there, during the electricial rough-in stage. HTH but not sure it did b/c I didn't give you a definitive answer. Sorry.

Edited to add ceilings are 10ft

Your island is long so I'd suggest 3 pendants about 18-20" in diameter. Lots of people on the board suggest blowing a balloon to the size you want and hanging from the ceiling to see what you think of the size.

Ideally, you will want the space between each pendant to be the same as the width or diameter of each fixture. For example, if you have 18 inch pendants, the space between each fixture should be 18 inches. This rule of thumb remains true, even if the pendants are hung at staggering heights. To determine the appropriate size of your kitchen island pendants, follow the steps below: Measure the length and width of your table, kitchen island, counter, bar, or desk in feet. Subtract 12 inches (or 1 foot) from each of these measurements to ensure there is 6 inches of clearance on all sides of the fixture. Take the remaining measurements in feet and add them together. This number is the approximate width allowable of each pendant. To determine the allowable number of pendants over your desired surface, take the length of your table and minus 12 inches and then divide by any number under the maximum allowable width (as determined in the previous step) and divide by two. This number is the approximate number of pendants that you could hang over your kitchen island, dining room table, or counter-height bar. So I'm getting 18 inches is a good size. But my math may be off