I purchased a Giant OCR-2 (next model up from OCR-3), last year I put over 2000 miles on it between Aug - Dec. Some of the riding included a 200KM brevet, 2 125+ rides and 6 or 7 century rides. As for the frame and components, the OCR-3 should be fine, however as money comes available you will end up wanting to do some tweaks to it to make it more comfortable for rides greater then 100 mile. (Which is probably true for most bikes.)

The OCR-2 I have will also except a rack, I assume the OCR-3 should also since they both use the same frame.

For LD riding, you will want to dump the stock saddle quickly, also the factory brakes will not last you long if you are doing a lot of hills. I just go a new Brooks B-17 in the mail yesterday, hope to have it broke in for a 200K Brevet in March.

I logged the maintenance I did on the bike for the first 2000 miles, can't say if your experience will be similar, but it may give you some insight. If you are interested, here is a link to my log, the service record is in the middle column. http://www.mycyclinglog.com/bike_detail.php?bid=2011

Like others here, I would not recommend doing LOADED touring on it. For credit card tours / brevets / centuries it is fine. As for using it as a LD/Randonneur bike, I have read that 1200KM rides are completed every year on just about every type of bike imaginable. A lot of times it is more an issue of having your head into it rather then equipment.

Other modifications I have considering for doing LD riding with the OCR-2. These may be similar for the OCR-3.

#1 - Aluminum seatpost, I weigh 225, plus I would like to dump the Bontrager rack and hang a good size bag off of the back seat. Not sure if it is a good idea on the Carbon Fiber Post. I figure I will still keep the CF post, and put it on for rides less then 100 mile. Rides longer then that I will reconfigure to use the aluminum seatpost / bag combo.

#2 - Brooks Saddle - Received yesterday, throwing away the stock saddle.

#3 - Some say that the rims should be upgraded for Brevet riding. I am still out on this, the stock ones on the bike are 24, and are pretty durable, and have only went out of true one time due to a pot hole that I hit at good speed.

These rims do propose a problem with using a generator hub though. For 300KM or longer events you will have address this issue and consider getting a different set that supports the hub, or going battery powered for your light setup.

Based upon my experiences, I think the bike you have will be fine. Just make sure it fits you, and be meticulous about its maintenance.