I'll give a quick comparison of cuben vs. silnylon with regards to this application, and then compare the main shelter options being discussed here.
Cuben vs. Silnylon:
For the tarp, both materials are going to be plenty strong. Cuben is going to fare better in wet, sloppy conditions since it doesn't sag and it's extremely waterproof. Silnylon is going to be waterproof enough...especially for the first few years, but it will sag in extended wet/high humidity which means re-tensioning. It kinda sucks waking up to a saggy tarp. Cuben is also going to save several ounces. Silnylon may be better for snow loads due to it's slipperiness aiding snow shedding.
For the inner, sagging is not an issue since these fabrics are just used for the floor. A heavier grade of cuben (1.2 or 1.5oz) is going to be more waterproof than silnylon and non-slippery, but the weight savings are none because heavier cuben is being used. In this application, it's mostly about cost, slipperiness and waterproofness. I prefer cuben, but it's not a big deal because there's no weight difference or sagging issue. A silnylon floor is likely a good way to save money if you don't mind adding some silicone dots to the bottom of your pad to combat the slipperiness.
Before I really get into this, I'll spoil the suspense and say that what you really want is a cuben tarp with an integrated or removable beak, and a silnylon inner tent.
I was going to break down all the options mentioned by weight, price and pros/cons, but once you start considering mixing a tarp from one maker with the inner from another there just gets to be too many configurations.
IMO, some sort of a beak on the large end of the tarp is really valuable because it's going to handle foul weather much better. On a lot of trips you can get away with no beak, but it's really nice to have the option for wet or winter trips. And honestly, I fall asleep a lot better with a beak mostly enclosing my tarp because I'm not thinking about how easily a bear could snack on my head without me even waking up. This isn't a likely or rational concern, but I sleep better with a beak. It feels more like a tent if you want it to.
As previously discussed, I also think you want cuben for the tarp because it's non-saggy and going to save quite a bit of weight. Buying a cuben tarp is cheaper than buying a silnylon one if you're going to wind up upgrading to a cuben tarp next year. The extra waterproofness is a bonus.
So with that said, I wouldn't buy the cuben MLD Grace Solo Tarp, because the HMG Echo I tarp is $5 less ($270) and it gives you the option to add the beak (2.8oz and $90) now or later. The HMG tarp is slightly heavier (6.1oz vs. 5.9oz w/o guy lines) because they've super reinforced it and because there's snaps for the beak.
Another cuben tarp option that has a front beak is the Bear Paw Canopy Tent. You can get this with a rear beak as well to make it more enclosed which is pretty cool. You can get it with a partial coverage non-zip front beak, or with a full coverage zippered beak like the Echo I. The main difference between this tarp and the HMG Echo is that the beaks are not removable. This is a good thing if you'll always want them, because it eliminates some snaps and cord (weight and complexity) but it's a downside if you'd like to have the option of going really light with just the basic tarp on some trips. I like the rear beak. I'd get that and the full zip front beak. With the full zip front beak (like the Echo) you're looking at $325 vs $360 for the Echo I tarp + beak. So you'd save a few bucks, but you'd lose that savings if you opted for the $30 rear beak. This tarp is available in 0.51oz cuben as well (vs. 0.74) which saves 2.5oz. I'd get that if you're hiking in mellow areas, but if you're heading into the mountains I'd stick with 0.74. Weight is 9.5oz but a bit more if you get the full zip beak and/or rear beak. Get the HMG if you want a removable beak. Get the Bear Paw if you want a rear beak. The Bear Paw canopy tent is a bit bigger, since it doesn't taper in width. So you kinda need the rear beak with this, but you don't really with the HMG as it has a much smaller rear opening.
The last two cuben tarp + beak options that I'm aware of are the MLD Patrol Shelter in cuben ($305) the Yama Mountain Gear Cirriform tarp ($300-$450). The Patrol shelter has a back wall which is nice. Both tarps use a non-zip half beak and a tapered shape (narrower at feet end)
You've got a lot of options for bug tents and they don't vary that much. You probably want a silnylon floored one because they're not any heavier and you'll save money.
The HMG Inner is expensive ($220) and kinda heavy (11.5oz) because the 1.5oz cuben is a bit heavier than silnylon (about 1.3-1.4oz once treated) and because it uses a lot of heavier shock cord. I replaced this with lighter stuff and saved about 1.5oz as I recall.
The Yama Bug Shelter 1.25 is a nice option (10.5oz, $119) if you're looking for a bit bigger option than the MLD Serenity Shelter (8.5oz and $135). Get the MLD Serenity with a bug netting door if you're using a beaked tarp. The Bug Shelter 1.25 might be a little wide though to fit under the HMG tarp and probably the MLD. At 42" wide at the head end, you wouldn't have much tarp overhang with a solo tarp. You'd probably want a 1.5 or 2 person tarp.
So to cut the point and give my $0.02, I'd recommend:
1) cuben MLD Patrol Shelter + MLD Serenity Shelter - If you want a non-removable half beak. $440 & 15.3oz
2) cuben Bear Paw Canopy Tent + MLD Serenity Shelter - If you want a non-removable full beak. $440 & about 18oz
2) cuben Bear Paw Canopy Tent + Yama Bug Tent 1.25 - If you a larger inner and non-removable half or full beak. $456 & 20oz.
3) HMG Echo I System - If you want a removable full beak. $495 & 21oz or $495 and 19oz with MLD Serenity Inner