it will be ok, as mentioned above, 1 lane for air tatoo traffic, one for other destinations. Should be alright after the fairford turning too
To be honest, it can get pretty bad down there. Personally if I were going from Swindon I'd go via Bassett and Ashton Keynes ... but that's just me :-)
The road comes out on the Preston Tollbar - which is the turning you want for the ground.