I have a number of tarps and found it can sometimes be difficult to protect ends from blowing rain with hex shaped or diamond shaped tarps. Wet sleeping bag, quilt, or underquilt can make for uncomfortable, long nights. Now I prefer a tarp with doors.

I was curious to learn how much a tarp with doors would add to the overall weight. Given that you are considering a cuben tarp, I calculated potential weights to see what the savings would be using an 8x8 vs. a tarp with doors. Here's what I found based upon z-pack listed weights:

(a) Tarp with Doors

Oz -- Item
6.50 -- Tarp with doors
0.12 -- stuff stack
1.76 -- spectra cord 1.5mm (0.88oz per 50 ft) x 2

2.84 -- MSR ground hog stake (regular lenght, 0.71oz per x 4)
OR
1.12 -- Vargo outdoor 6.5in shepherd titanium 0.28oz per x 4

TOTALS
11.22 -- total with ground hog stakes
9.50 -- total with titanium stake (less holding power than ground hog)

(b) 8x8 Tarp (no doors)

Oz -- Item
4.50 -- 8x8 Tarp
0.12 -- stuff stack
0.88 -- spectra cord 1.5mm (0.88oz per 50 ft) x 1

1.42 -- MSR ground hog stake (regular length, 0.71oz per x 2)
OR
0.56 -- Vargo outdoor 6.5in shepherd titanium 0.28oz per x 2

TOTALS
6.92 -- total with ground hog stakes
6.06 -- total with titanium stake (less holding power than ground hog)

Differences in weight

11.22 - 6.92 = 4.3oz with ground hogs
9.50 - 6.06 = 3.44oz with shepherd stakes

The total weights don’t include supplemental items such as cord tying gadgets (e.g., Dutch tarp flyz, knotbones). Nevertheless, I may have missed an item or two that could add to differences in weights.

Looks like going with an 8x8 tarp will save about 3.44 to 4.3oz over a tarp with doors.