Thermal Boiler produces 800mB Steam/tick (stated on Large Steam Turbine page), this is a static value.
Large Steam Turbine consumes 1600mB Steam/tick
Lava bucket consumption times are not listed because we (the end users) do not currently have exact numbers.
Below numbers are from a combination of statements made over recent weeks and math done in my head right now.
At 0 heat, consume ~ 1.6 Buckets/second Lava, approximately 1 Bucket every 12 or 13 ticks [this is the math we need the most confirmation on]
At maximum heat, consume 1 Bucket of Lava every 75 Ticks (30,000EU / 400EU/t = 75t)
400EU/t comes from Large Steam Turbine producing 800EU/t @100% effic., 2 Boilers = 1 Turbine
the level of complaints about all this is making me almost want to set up a workspace, decompile GT, and dig the math from it by hand...