I also live in Bristol and do the trip to and from St. Marys regularly, and whilst I have done it in an hour and 10/20mins a few times, I'll be amazed if anyone does it in under 2 hours on a friday evening. There may be no fixed speed cameras, but they often put mobile ones on bridges over the M4, so look out for them. And the last few times I've done the journey there have been 50mph average cameras on the A34 - not sure if they're still there?
Although there is plenty of on-street parking if you're prepared to walk 15-20mins, I'm told there's a big fireworks display going on somewhere nearby so that might make it a bit harder.
And about picking up tickets at the ground, living away from St. Marys I have to do this a lot for away games, most of the time you have to wait until about 20-30 mins to kick off before they arrive and are dished out, although at Norwich last year we didn't get them until 5 minutes before kick off! The difference is this time I imagine they'll be loads of us wanting to collect, so hopefully they'll have a system in place to deal with it.........