Because turbo will always lug, therefore V6 is better
Actually that lag is only present with high-pressure turbos. If they would use a low-pressure turbo there would not be any lag in the application of boost.
Volvo used low-pressure turbos on their engines in 2000 (I have one) and the power application is smooth. If you are unfamiliar with low vs high pressure turbos, the low is virtually always "on" therefore you don't have any lag before it starts boosting. You would think "always" being on would hurt the longevity, but there isn't any more degradation as far as I have read or experienced myself.
Longevity depends on how you care for it. Good quality oil, mainly sythetic, and good change intervals will keep the turbo from coking up. The intercooler is simple enough to be left alone. I NEVER performed the turbo cooldown after a drive EVER and nothing detrimental happened to the turbo. They are fairly simple machines.
As opposed to our 6's or the DI I4's here those turbo'd engines DO need 93+ if you really want to get full power out of the engine. That higher compression from all that air really does need that octane. It'll run on 87 but why would you? Let's not turn this into another octane thing though, just concurring that there's your extra cost with a turbo.
As far as extra heat during full out running up hills, long range drives, etc. I can't speak to that. This was a daily driver. Although when I was on another forum for Volvo, there was very little talk about poorly operating turbo's or massive numbers of failures because of a turbo cooking itself. So that extra cost might be caused by how really hard you run it.
Compared to the 3.5 6 in my car now, I get comparatively the same MPG. 33 for the turbo 1.9l I4 5 speed auto(160 hp) and 31 for the 3.5l V6 (278+ hp) 6 speed auto. MPG done old fashioned way and I did say comparatively the same considering the output numbers on both engines and size of engine.
Actually I have more concern about the VCM on this engine causing problems vs a turbo. BUT it's all how you take care of it. If a turbo goes bad it's purely a plug 'n play fix. Not cheap, but easy (kinda like my last GF
). VCM goes bad, well I'm not gonna think about that but as far as I can see the mechanics of VCM don't appear to fail. The application of same might screw around with other systems and parts like plugs possibly fouling
My .03 anyway.