OK, I am going to assume this is not a troll post and will give you some real advice.
When I "ran" the Ascent a few years ago, I felt great up to about 10,000 feet. Then the altitude hit me like a brick wall. I hadn't trained above Barr Camp and boy did I pay for it.
No, 5:00 per mile slower is not reasonable. Someone who can run 6 minute miles at 6,000 feet is not going to be able to complete the Ascent in 2:13 (11 minute mile pace). Based on your question, I feel you have no idea what you are undertaking.
Someone who has trained optimally, such as Matt Carpenter, can run the Ascent faster than they can run a marathon at sea level. Carpenter's marathon PR is something like 2:18, but his best Ascent time is 2:01. For most people, however, their Ascent time will be somewhat slower than their marathon PR. For some unfortunate souls, the Ascent time will be more than half an hour slower than their marathon PR. I feel, unfortunately, you may fall into this latter category due to your lack of proper preparation.
For example, suppose you can run a half marathon at 6,000 feet in 1:25 and a full marathon in 3:10. If so, I think you'll finish the Ascent in something like 3:30-3:45.
My advice to you is to spend as much as you can hiking on Barr Trail near the top. Drive up to the top and walk down 1-2 miles, then walk back up to the top. If you still have energy, feel free to jog. Once you hit the top, repeat the whole routine if you can.
Do this as many times as you can before race day. If you go up to the top at least three times, I promise it will make a HUGE difference.
Equally important, take it really easy for the first 10 miles. Leave something in the tank for the last three miles. You will need it. Make sure you bring water to carry with you as there will be a long stretch with no aid stations. (The three mile stretch between Barr Camp and A Frame may not seem like much, but it could take you cclose to an hour, which is way too long to go with no water.)
More generally, I think you should ask around town and talk to people who have done this before. I think you would benefit from getting information about hydration, clothing, training, etc.