In reply to mypyrex:
The issue is more about being able to cope with day after day of walking with no or little respite rather than being able to do some mammoth day. Because little aches and pains accumulate. But you will know that since you have done treks before.
Its an excellent idea to have a target ahead of you and particularly something worthwhile like this.
Only you know what state your body is in now and what you can realistically achieve.
A professional guide can only do what Management Consultants are meant to do and put your words in their mouths.
You have enough experience to work out now whether it is realistic and you have the guts and ability to succeed so go for it, well done, good luck and keep us posted.