I hunted down their 2011's chart...
http://www.profootballweekly.com/2011/04/06/pfws-exclusive-draft-value-chart-4
They had a few big misses but it's pretty accurate. I was expecting to be able to tear it down.
When they miss in round 1 or 2, it's usually just by the next tier (1B vs 1C). By round 3, it is more like 2 tiers (3C vs 4B). In the first two rounds, here were the only misses greater than 1 tier...
MOVED UP - 10
Christian Ponder went 1B vs 2A
James Carpenter went 1C vs 2B
Colin Kaepernick went 2A vs 3A
Brooks Reed went 2A vs 3A
Bruce Carter went 2A vs 2C
Ben Ijalana went 2B vs 3C
Stefen Wisniewski went 2B vs 4C
Orlando Franklin went 2B vs 3B
Marcus Gilchrist went 2B vs 3C
Jonas Mouton went 2C vs unlisted
MOVED DOWN - 9
Aaron Williams went 2A vs 1B
Da'Quan Bowers went 2B vs 1C
Stephen Paea went 2B vs 1C
Randall Cobb went 2C vs 2A
Allen Bailey went 3C vs 2C
Johnny Patrick went 3C vs 2C
Christian Ballard went 4A vs 2A
Clint Boling went 4A vs 2C
Dion Lewis went 5B vs 2C
A few guys dropped big and I didn't count them -- late drug concern (justin houston), or there was a medical issue (marcus cannon and virgil green). Pretty dang accurate. By Day 3, it becomes very hit or miss.
Assuming their sources are similar in 2012, it seems plausible that McClellin can jump up to 2C...maybe 2B...but jumping to 1C would be a shocker. Small sample size, but PFW was very accurate for round 1 in 2011.