I6 or V8

[Fraser]

Give me a break! Writing off the V8 because it isn't perfectly balanced is like saying that Kim Kardashian is unbalanced because her left nipple is two microns bigger than her right nipple.
The fact is that both the IL6 and the V8 (being a 90-degree) have perfect balance of the primary and secondary inertial forces, the big factors in determining if an engine is smooth or not. And while the IL6 also ticks both boxes in terms of perfect balance of primary and secondary free moments of inertia whereas the V8 scores a '10 out of 10' for secondary free moments but only an 'eight of ten' for primary free moments, is no big deal either way.
On the consumption issue there's so little in it that it's irrelevant. Much more significant is the fact that the V8 is more immediate in its response and a much better 'drive'. I could live with a 6 but only with a manual, preferably the post-'04 six-speeder. For me my '05 3.0d beats the pants off the petrol six or either 4.4 but that's another story and irrelevant here...