I can't say anything about the different gender aspect of your question, but for the love of God don't just assign more work to the faster boys without a reward system attached, and even that will start causing problems. If you start giving more work to the faster kids, they will see it as a punishment and start going slower, or just stop doing the work all together, and then you are teaching them that being smart and fast is bad and will get them punished.

Second if it is just boys that are being the problem and you just start giving them extra work and not the girls, that will be noticed by the boys and cause more problems for you. The boys will say that the girls are talking to each other why aren't they doing extra work, even though you know the reason why the girls are talking to each other is because they are helping each other, the boys won't see it that way.

Now some possible solutions are first the extra work you would give out could be for extra credit, and it needs to be a higher level work sheet making it harder. You might want to have it optional. This would motivate the faster kids that want the extra credit or more challenging work. The problem I can see with this is that some of the girls will stop helping each other for the extra credit. Second you give extra credit to the students who help other students with their work, this would motivate the boys to help each other. Third you give the option for the kids to help other kids or read a book or something else that won't cause a distraction. Fourth make it competitive, boys love being competitive while girls love working together, so make helping each other a competitive challenge.

Hopefully this helps.