It is important to note that a pure Lightning Bolt "rotation" may
generate more dps than a Lightning Bolt/Chain Lightning rotation. This
is due to a few factors, mostly in-game latency and "user lag". If there
is an extra delay in your rotation from switching to Chain Lightning
and back to Lightning Bolt, this will reduce the effective DPS gain that
we would expect to see from using Chain Lightning with its shorter
casting time. You can use addons such as
LagInfo to see what your user lag is. Reducing this will increase the time spent casting, and thus increase DPS.
General recommendation
If you have the mana, prior to getting 4pc T6 a CL rotation is the best
way to go. After you get the 4pc bonus, switch to LB spam, and
regem/gear appropriately.