I think T5 is about $1 per quart cheaper than T6. I use the T6 in everything since it is rated for gasoline and diesel engines. I find the convenience of not having to stock multiple oils worth the extra cost. Also T6 goes on sale at least once a year with a rebate coupon for about $15 per gallon. I like the fact that the T6 is a 5W-40 weight. I do have one car that specs a 5W20 oil but I refuse to put a 20W oil in any engine that runs in the south in the summer (or winter for that matter). These companies will do anything to get an additional mile per gallon EPA rating, including possible damage to their engines in the long term. As long as they last past the warranty period (24K in some brands) that is all they need for it to do.
I don't care if my car gets 31 MPG (which is does with 5W-40 T 6 oil) or 32 with the 0W-20, 1 MPG wont break the bank for gasoline purchases.
Call me OLD and Out of touch if you want but I have always ran 10W40 (prior to using the full synthetic oil)oil all my life and don't plan to change now. I do go with the lower cold start value like 5W or )0W if I were in Canada, but the hot oil rating, I want to be at least 40W.