Turbo engines can, in theory, work more efficiently, as you can get more fuel/air into the engine per combustion cycle.
However, the problem is the enrichment, which results in much worse economy when on boost.
My car is a turbo, and I have made pretty good fuel savings. I would say go for it, but you would need a wideband Lambda sensor in order to avoid the enrichment (it happens a lot earlier on turbos, I think), and a SuperMID would also be good!.
The smaller the turbo the better as it can help get more torque - my boost goes above 0 at 900-1000rpm, for example
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