For a 10mil barb offhand (assuming it was really worth 10mil), if you add 60-70 str you are definitely adding something in the area of 10-30mil to its value. Now without the str I still think it would have gone for a lot more than 10mil anyway, which makes the whole thing make a lot more sense.
Also, never go in bid wars. Bid last 5 seconds. You should know that by now that you can only benefit from doing so. Bid wars compared to bidding last 5 seconds guarantees you to pay at least as much as you would have paid if you bid last 5 seconds, so just don't do it.