Well! After finding out that double cracking my Raw Oil will just about double its EU value, I went ahead and built several Large Gas Turbines. Replaced the Diesel Engine that was powering my base, redid all the wiring and fluid pipes to fit. And here's what I found out:
The Diesel Engine costs more than 400 Titanium to build. The Large Gas Turbine costs 160 Stainless Steel and about 250 ingots of other alloys made from fairly common elements.
The Diesel Engine, when supplied with oxygen to boost its output, immediately outputs 6k EU/t from an IV Energy Hatch, slingshotting you into the Insane Voltage era. It is very low maintenance, just needing Lubricant, Oxygen, and some fuel piped in continually. There is also no downside at all to supplying it with oxygen.
The Large Gas Turbine, when you're first able to build it, produces between 2k and 3k EU/t. And to get it to produce that much, you'll need to spend another 75 ingots on a Large Turbine Rotor item. (
Someday I'll have to add a proper table of turbine materials to the wiki, but According to this table I just made, Fluxed Electrum is a decent early choice, Thaumium or Black Bronze will do in a pinch, and HSS-S or TungstenCarbide are pretty good if you can spare them.) The Turbine Rotor item eventually wears down over hours or days and will have to be replaced - a Needs Maintenance cover will help you to automate replacing the turbines. Also, the Gas Turbine will greedily eat up to 25% more fuel without producing any more energy, unless you fit the input hatch with a Fluid Regulator cover.
Both generators have great fuel efficiency compared to the HV-tier generators before them. Diesel Engine when supplied with oxygen increases fuel values by +50%, compared to the -15% on the Turbo generator. The Large Gas Turbine's efficiency depends on its rotor, which initially ranges from +20% to +40%. Still a great improvement over the -15% on the Turbo turbine.
After you are well into the Fusion era, the new materials available will allow you to make things like Huge Duranium Turbine Rotors, which can get the Large Gas Turbine up past 4k EU/t.
When taken together, all of this points to the Diesel Engine being much easier to set up for a much greater immediate benefit, at the cost of a pile of Titanium that you might not have lying around for it. And the Large Gas Turbine is a bit cheaper to craft, a bit more involved to keep running, but it becomes stronger the later you are in the game.
EDIT:
Turbine materials table is done!