I don't know how isolated the issue is, but with the previous Keyboard & Magic Trackpad, whenever I connected my bluetooth headphones (Beats Studio Wireless) to my 5k iMac I would have severe lag issues on all peripherals, making them unusable. I suspect the remedy is due to the new LE bluetooth.
Just thought I'd mention it for anybody else who faced this issue.
Just thought I'd mention it for anybody else who faced this issue.