Great Circle Mapper shows the GC passes over Scotland anyway so it looks like a winner route-wise (vs any other EU hub).

You could do AC/GF most days with an 85 minute layover which maybe within the MCT (both flights use T3), or AC/BA if money was no object but given this would save little more than an hour I would personally prefer the peace of mind of a through ticket and stick with BA all the way through, arriving/leaving T4.