How long will my 2005 ford Mustang v6 last?

I have 81500 miles on it now never replaced anything other then regular maintence such as oil change every 5k and did a tranny fluid change at 75k. I try to keep rpms under 2k I have overdrive on it! And i'm not a speed freak because of gas milegae! About twice a month I'll race someone at a red light! I have a cai, headers, exhaust! I'm thinking I can get around 150k put of it before a major repair any ideas on this?

300k easy

With regular factory-type maintenance, 200,000 should not be a problem.

I drive a 2005 Mustang GT that i've owned since almost brand new. To answer your question:
It will depend on the types of preventative maintenance that you do. As with any machine if one part starts to go bad and puts strain on other parts, you end up having repair jobs/mechanical failure. I would recommend that in addition to what you are doing, you also clean the fuel system about every 15-18k miles, only use non sulfur based low range gas (e.g. 87 octane, nothing above 89 octane). On Mustangs from 2005-2009 the fuel pumps have a tendency to foul up if they are used with cheap sulfur based gasoline (e.g. Arco, most cheap gasoline, etc). Running the fuel cleaner through a full tank of gas as I mentioned above should keep you from having problems in the future.

If you haven't done so already, I would inspect and/or replace the Serpentine Belt. You could also further extend the life of your engine by using a synthetic blend motor oil. It puts less wear and tear on your bearings and rings and you can safely go 5K miles between oil changes (I recommend Penzoil for this car). You might consider also replacing the spark plugs and testing the coil pack as well based on your mileage.

Keep in mind on these cars there was a Technical Service Bulletin on the spark plugs. They have a tendency to fuse inside the engine and break when you try to remove them. Its best to have them changed by a licensed and insured mechanic or at the dealership. They can put an anti-seize gel on the plugs so they won't fuse again.