Will a slightly taller tire only in the rear mess up the abs and traction control ?

No.

Agree with Fantastic from what I have read. 2012 and newer it will throw off your Speedo a bit because it uses the wheel speed sensor/ring and it will think the bike is going slower than it is due to the larger circumference. Mine is already a bit off so I say go for it. I will be doing a 200/50 or 55 next time depending on how things go. If I ugrade to Carrozzera's maybe I will get the 6.25 rim.