The opportunity to play left tackle (along with a hefty pay raise) may be the only important factors to Saffold.
If you were in his shoes what else would you consider?
Well first of all he's going to get a pay raise of substance so some of the things he might consider are, weather , income tax rates or absence thereof (Seattle,Florida teams and Texas teams can brag NO state income tax, Cali is 10.5%) Missouri is mid range
http://taxes.about.com/od/statetaxes/a/highest-state-income-tax-rates.htm,
chances of making the pro bowl .......here IMO we have a decided advantage,he will never make it as a tackle and most everyone coming after him will be after a tackle, but if we throw some incentives in and promise to keep him at guard barring injury IMO he makes it next year and could become a perennial Pro Bowler,which FWIW brings a chance at HOF should this team gel around him.
Proximity to home could be an issue as well he's from Ohio which has teams ,played at Indiana so could be a Colts fan,in the end there will be a market set for him as the 6th best tackle available, then we'll see.
I can't imagine why he'd want to return to LT other than the money.