"So what about starting at Roads End up to Lake Reflection over Harrison Pass to Lake South America over Forrester and back."
That would work, Ken.
"Harrison is quite steep on the north side with it being steep with a considerable scree slog for what it looks like 2000 feet."
Harrison is mostly talus, with not a lot, if any, scree as I recall. It will be strenuous, especially at the top, but not exposed. It is class 2.
"Am I biting off more than I can chew or should I just go over Avalanche to Colby then over Forrester and back?"
If you were comfortable on Lamarck, you'll do fine on Harrison. I think the Avalanche/Colby route would be a lot of unnecessary extra trail miles, enough extra to ensure that you would be hiking all day, every day, for the entire 7 days. It would also drop you down into Kern Canyon, 8000' elevation at Junction Meadow, and then you would have to climb back out, a hot dusty hike in August. Also, when you're down in Kern Canyon, you are not going to see much of anything. If you go in over Harrison and follow the trail from Lake South America on down to the JMT connector trail just north of Milestone Basin. you'll be traversing some of the most awesome real estate in the entire Sierra, with spectacular views at every turn. It is enough shorter to allow for a day in Milestone Basin, which I would very highly recommend, for reasons I stated in an earlier post. From the Jmt connector trail, you could be over Forester Pass in one day and another day or so would have you back to Roads End. That would be a great loop for you.
Edited for content.