Mixed Tires

[X5Kiwi]

My 4.4i X5 currently has Yokohama Advan ST tires, with 275/40R20 on the front and 315/35R20 on the rear.

My front tires have about 4mm tread, but have worn badly on the outsides, the left front now having a bald strip about 4 cm wide.

However the rear tires are fine, about 5mm even tread on them.

I have found a good deal on some Hankook Ventus RH06 tires for the front, however I am wondering if there is a downside to having different brand tires on the front and rear? The Hankook tires are MUCH cheaper than the Yokohamas, and all the reviews I have read show they will perform nearly as well.

We don't really get snow on the roads here in New Zealand, so we generally run the same tires all year around.