If I am reading the rules correctly these contracts will begin at the expiration of the old contract, therefore:
Tyler Seguin, $3.8m (2012-2013)
>>> 2011-2012 = #11C #17RW >>> 2012-13 = #14C #10RW >>> #11C = 7.2m per.
= Tyler Seguin, $7.2m (2016-2017) (4 Years)
Patrice Bergeron, $4.5m (2012-2013)
>>> 2011-2012 = #12C >>> 2012-2013 = #23C >>> #12 C = 7.1m per.
= Patrice Bergeron, $7.1m (2016-2017) (4 Years)
Milan Lucic, $4.1m (2012-2013)
>>> 2011-2012 = #15LW >>> 2012-2013 = #24LW >>> #24LW = 5.9m per.
= Milan Lucic, $5.9m (2016-2017) (4 Years)
Nathan Horton, $4.0m (2012-2013)
>>> 2011-2012 = #90RW >>> 2012-2013 = #44RW >>> #44 RW = 2.8m per.
= Nathan Horton, $2.8m (2015-2016) (3 Years)
The difference between the new and old contracts is equal to +6.6m. Therefore I need 6.6m in space which will be cleared when the new contracts take over and the hits against my cap are processed, I will have 9.1 in buyouts clearing plus Tim Thomas for 5.0m.