So, you have gotten two “not a problem” answers, now you are going to get the maybe yes – maybe no (long winded version).
I am going to start with your 6500 miles on the rear. 6500 miles might not be too bad depending on your driving conditions and driving style.
- Driving in really hot weather (hot asphalt) tends to have the air in the tire expand causing a higher pressure – can cause premature tire wear.
- using a lot of rear brake when stopping or jack-rabbit starts causes extra tire wear
- hilly country (foothills, mountains) requires more torque to the rear wheel, thus more tire wear
enough about why your tire may have only gotten 6500
different brands. You won’t find many Bud drinkers who would jump back and forth between Bud and Miller and Coors and . . . Even within a single brand a “lite” beer isn’t the same as the “real” stuff.
like beer, not all tires are made the same – different softness & sidewall construction – even within a single brand.
- most people are aware of different softness in tires – softer tires have more grip and less durability (get fewer miles). Most racing shops and many good automotive shops have a gauge you can buy to test how soft a tire is – looks something like a tread wear depth gauge only with a sharp point for going into the rubber. Your rear tire has already had more than one heat cycle on it (like a scuffed tire on NASCAR), so find a Dunlop like your rear tire and measure the hardness, then measure the hardness of the one the dealer wants to sell you. You now have something to look at when looking at other brands.
- sidewall construction (including radial – non-radial tires) determines how the sidewall will flex, especially under hard cornering or braking – you want the front and rear as close as possible. If your front sidewall is softer, you can find the front end trying to “push up” in hard cornering or when braking in corners. Nor do you want the rear of the bike to get squirrelly in the middle of the corner from the rear sidewall being softer. Not many people are stupid enough these days to mix radials with bias tires. You will probably have to go to the manufacture’s web site to get sidewall construction specs.
My advice – do your homework and if you go with two different brands or two different lines within the same brand, do it with your eyes open not based on "a guy down the road heard 'bout a fella who might have dun it". 
Hope this helps
PS: I spent a dozen years turning wrenches on stock cars – there are only 4 things that keep a stock car on the track and moving forward – the 4 tires – you gotta know about them to look after them.
When workin' on your ride the first tool out of the box should be the manual