I have only put carpet in two boats so I'm no professional by any means.
We looked at the pre-cut carpets for both boats and we came to same conclusion.......
The pre-cut leaves very little room for error if you make one.
2nd. It was much easier to get a good 20oz carpet localy cheaper and not have to pay outrageous shipping prices.
3rd. We were able to see the color and feel the carpet we were buying before laying out the bucks.
Like I said I'm not a pro in the carpet area and these are just a few things we thought of when looking for ours.
Good luck with your project and be sure to post some pics while your doing it.