Pittsburgh to DC in two days
 

I have set a goal of riding the GAP and C&O in two days next year then an easy ride back my biggest concern is the condition of the C&O I know the GAP side is easily doable but most of the reports I hear about the C&O is that it is fairly rough but they are all from people that rode it a couple years ago. Any thoughts or ideas?

I like it. I did 3 days a couple years back and have entertained thoughts of trying a 2-day version.
You won't like my answer, but this challenge depends entirely on weather the 2-5 days before.
If it rains a lot, you'll be hard-pressed completing 100 miles in a day, much less the 175-ish needed.

If dry, the C&O can be fast, BUT it takes much more attention to hazards that can come up quickly. I did southbound, hitting the C&O when I was getting really bored of the trail. I nearly endoed from giant rocks, roots and washouts several times. There's no spacing out on that trail.

The weather is a concern I plan to go late August early September to avoid the rain

Beautiful weather in late summer brings crowds of people. I rode in mid-May and there were still so many people in places like Ohiopyle that I nearly had to get off and walk. YMMV

Tire size is important. I rode on 35's on a cyclocross bike. great ride....We did it in May...lots of mud, roots, and rocks. 3 day trip.

Late August can bring thunderstorms. When I rode the GAP as part of a cross-PA trip starting the Saturday after Labor Day is rained for a few days before my arrival in PGH that Friday, but the trail was pretty much dry by Saturday. Saturday was pretty warm and sticky, with a moderate headwind in places. Later in the trip, near New Berlin, PA, a massive thunderstorm moved in from the south while I was in camp. Sheets of wind-swept rain for at least 35 minutes. Thought I would emerge from the laundry building to find my tent blown into the pond it was pitched near.

Met a guy in Frostburg, Md earlier this month riding a fixed gear, no rack, no water bottles on bike. Lightweight backpack only. 2 days on the C&O, 1 day Frostburg to Pittsburgh. In the middle of a bit of a dry spell in the Potomac watershed. He knew what he was doing for sure. I watched him climb the very steep hills up into Frostburg and back down to the trail late in the afternoon just for the ride and to get a few extra miles in before crashing in the bunkhouse at the Trail Inn in Frostburg for his last overnight.

Also, do highly recommend Frostburg as a stopover. Quiet, scenic, town has restaurants, coffee shops, pubs, music, etc. Great inn, bunkhouse, campgrounds, fried chicken at the Trail Inn.