Ok, so let's take a look at Aaron Rodgers' first 8 games vs. other historic QB seasons through their first 8:

Rodgers (2011): 192 for 265, 72.5%, 2619 yards passing, 9.9 ypa, 24 TDs, 3 INTs, 37 carries 127 yards, 2 rushing TDs. 129.1 passer rating
Brees (2009): 181 for 265, 68.3%, 2336 yards passing, 8.8 ypa, 17 TDs, 7 INTs, 17 carries for 28 yards, 2 rushing TDs. 106.1 passer rating
Brady (2007): 198 for 267, 74.2%, 2431 yards passing, 9.1 ypa, 30 TDs, 2 INTs, 12 carries for 25 yards, 2 rushing TDs. 136.2 passer rating
Manning (2004): 179 for 269, 66.5%, 2429 yards passing, 9.0 ypa, 26 TDs, 4 INTs, 15 carries for 38 yards, 0 rushing TDs. 121.2 passer rating
Marino (1984): 166 for 250, 66.4%, 2390 yards passing, 9.6 ypa, 24 TDs, 5 INTs, 16 carries for -9 yards, 0 rushing TDs. 120.9 passer rating

Brees went on to set the single-season record for completion % (70.6%). Brady went on to set the NFL single-season record for passing TDs (50) and total TDs (52). Manning went on to set the single season record for passer rating (121.1). Marino went on to set the single-season record for passing yards (5084).

I think it's safe to say that Brady had the greatest first 8 games of a season in NFL history, followed by Rodgers' 2011. If Rodgers keeps up this pace (a big IF, since Brady fell off significantly in his 2nd half of that season), he'll break the single-season passing yards mark, total TDs mark, completion percentage mark, yards per attempt (in the Superbowl Era), and passer rating mark.

I think completion %, passer rating and yards per attempt (maybe) are doable. Total yards will be difficult because I doubt he'll play more than a half in games 15 and 16 if home field advantage is locked up - in Marino's last 3 games he threw for 470, 404, and 340 yards to close out the season at 14-2. Total touchdowns will also be difficult - Brady built up such a monster lead (30) in his first 8 games, but also tacked on another 5 in his last two games (throwing 75 passes across the two to go 16-0).

One bad game really throws a wrench in the whole thing though.