So I ended up doing 30 laps but it would not have been an issue to do a lot more (It was getting late and I stopped playing).
I got my math wrong above as I counted the encoded items (2 of them per run) so in reality you get 10 items per lap from G2 to G4 with 3 items in each collection. Rare are about 2 per run. So I got 300 items per run and did 3 runs of 10 laps each which is 900 materials. Of these 180 were rare and 720 were G2 to G3. So I got these materials for a time investment at Dav's of around 37 minutes (not counting travel time to and from the system and landing).
Trouble is that when I checked my materials cargo it just doesnt look like I got an extra 900 items! I have checked EDDiscovery and it shows my findings but when I check Inara for my cargo of manufactured materials they just look like they looked when I started. I have no way of checking so have to go by EDD.
What was a bonus was that my fuel was low and I was able to land on the nearest carrier and refuel to get back home. It was my first third party carrier landing and I got a buzz from that. I bought an FC on the beta blowout so I have played with one but never docked on someone else's. Very handy to have it there in the system as I didnt have to go find the nearest station and could fly straight home.
The encoded take varies between 1 & 3 in my experience then as you say there are ten scoopable items plus there is often 1 to 3 NPC ships circling overhead which if scanned from the turret might provide additional encoded.
I have moved away now partly because I was going to try and check something else out and partly because I was getting to the annoying stage where I was getting too many items show up that I had no room for.
When you target the item the info window in the bottom left of your HUD shows how many you have in the store and what the maximum capacity is (54/100 for example) so you can keep a rough check that way.