After looking at the O-Lines of several good teams, I have come to the conclusion that it doesn't matter what round that they are selected. It only matters that they were scouted properly and that the Line is able to enjoy some consistency!
Here is what I found out:
Buffalo Bills:
RT Jonathan Scott 3yrs 141st Overall 5th Rd
RG Eric Wood Rookie 28th Overall 1st Rd
C Geoff Hangartner 5yrs 169th Overall 5th Rd by Carolina
LG Andy Levitre Rookie 51st Overall 2nd Rd
LT Demetrius Bell 1yr 219th Overall 7th Rd
Cincinnati Bengals:
RT Dennis Roland 2yrs UDFA by Dallas
RG Bobbie Williams 10 yrs 61st Overall 2nd Rd by Philly
C Kyle Cook 2 yrs UDFA by Minnesota
LG Evan Mathis 5 yrs 79th Overall 3rd Rd by Carolina
LT Andrew Whitworth 4 yrs 55th Overall 2nd Rd
Houston Texans:
RT Eric Winston 4 yrs 66th Overall 3rd Rd
RG Chris White 5 yrs UDFA by Green Bay
C Chris Myers 5 yrs 200th Overall 6th Rd Denver
LG Kasey Studdard 3 yrs 183rd Overall 6th Rd
LT Duane Brown 2 yrs 26th Overall 1st Rd
Pittsburgh Steelers:
RT Willie Colon 4 yrs 131st Overall 4th Rd
RG Trai Essex 5 yrs 93rd Overall 3rd Rd
C Justin Hartwig 8 yrs 187th Overall 6th Rd by Tennessee
LG Chris Kemoeatu 5 yrs 204th Overall 6th Rd
LT Max Starks 6 yrs 75th Overall 3rd Rd
New Orleans Saints:
RT Jon Stinchcomb 7 yrs 37th Overall 2nd Rd
RG Jahri Evans 4 yrs 108th Overall 4th Rd
C Jonathan Goodwin 8 yrs 154th Overall 5th rd NY Jets
LG Carl Nicks 2 yrs 164th Overall 5th Rd
LT Jermon Bushrod 3 yrs 125th Overall 4th Rd
Except for Buffalo, these teams are doing fairly well this year at running the ball and protecting the passer.
For comparison, Buffalo at 3 - 4 has made 107 first downs, gained 783 Yds rushing, 1131 Yds passing and allowed 16 sacks.
Seattle at 2 - 4 has made 114 first downs, gained 542 rushing Yds, 1319 passing Yds and allowed 16 sacks.
IMO, Buffalo has enjoyed more stability on their O-Line but Seattle has performed as good or better in some situations.
I have 5 Left Tackles whose draft positions add up to a total of 500 even...which of course averages out to the 100th position which is the 3rd Rd 4th pick
Since Ryan Succop was drafted # 256 I will give the UDFA a score of 257
The NUMBERS:
RT: 632 / 5 = 126.4 -> 3.95 3rd Rd 30th pick
RG: 547 / 5 = 109.4 -> 3.42 3rd Rd 15th pick
C: 967 / 5 = 193.4 -> 6.04 6th Rd 1st pick
LG: 681 / 5 = 136.2 -> 4.26 4th Rd 8th pick
Of course this is a relatively small sample size, covering ~1/6th of the teams but it gives us a general idea that not every good Offensive Lineman has to come out of the 1st or 2nd round. Jason Peters and Kris Dielman are good examples of that.