I've gotta say...
I've never really considered speed cameras an issue in Swindon personally as there isn't actually that many... off the top of my head, the only one I can think of which I regularly see is the one on the 419 on the hill (which is a complete bitch if you're going downhill and you're just wearing your brakes away). I'm more concerned with mobile speed cameras here.
I pretty much stick to every 30 residential zone, 40 for all the interconnecting roads between the residential areas but I generally tend to break the 40's on dual carriageways like great western way and queens drive to a little extent.