Any pros an cons between a 18x51 and 18x54? Can decide between the 2.. is the 3in really that big of a difference performance/room wise?

IMO not much difference only in price, weight, and may need a little more power to push it. Cause of more surface area.

With 6ft of bottom surface touching the water, it's a difference of 216 square inches of additional surface area creating lift. Yes, it'll make a difference with a load. The more load you add, the more bottom touching the water (angle of the boat in relation to the water changes under power), and more surface area creating lift, so it could wind up being more than 216 for that additional 3" of width. Figure that 3" will add to your ability to plane more of a load with the same amount of power.

Eventually, the additional weight of a boat from the additional weight will gain less load carrying without increasing power, but going from 51 to 54" width is not that point. At most, maybe lose .5 mph top speed from increased friction (you might actually gain a little speed), but adding that third person and gear will mean you won't lose as much speed as the narrower boat. Yeah, the difference won't be huge with a 3" difference, but it'll be noticeable to most people.

Girth matters to the ladies, get the 54" if you're choosing between the two...

When I ordered mine the cost between a 51", 54", or 60" (3/16th bottom)was the same. the bottoms are cut (after you get above 48") out of a 60" width sheet. So if it were me, JS, if I didn't go with a 48" then I would go 54". the 60" just seemed to be less timber friendly. But I bet there are lots of different opinions on that subject too! BTW had a 18'x46", replaced with 19'x54" used same motor maybe lost 1 mph in deep water but saw gains in the mud.(should have gps'd it cause I am very pleased with it after the SETX Mud Run)