Interesting thread and good to see theres been sum good points put in so far.
Id prob choose a v8 over a v6. Mainly for the v8 growl (something so beautiful bout it).
I originally chose my v6 commodore for numerous reasons:
1) Fuel economy (i don't have the ltr ratio but i get 450kms for $30 worth of LPG)
2) Flexibility. I have decent economy on both highway and town, before you start to hit the reply button : A 4cylinder will have low fuel usage around town but high on the highway, a v8 will have high around town and low on the highway....so the v6 is a good compromise between both
The agruement that v6s are cheaper for performance applications is a different story though....
The cost for a v8 is cheaper for the simple fact that a stock v8 produces more power from the start, so adding a blower or upgrades to the engine will provide higher numbers... (or lower on the quarter lol). Even tho the l67 is a gr8 engine A v8 engine will still provide better figures after being modified.
So id have to say that for performance applications a v8 will ultimately be better than a v6 (or a 4cyl for that matter), BUT for economy and flexibility when it comes to fuel usage (highway and town) id PERSONALLY prefer a v6...
I originally was going to modify (supercharge and sum mild engine work) my VR v6, but upon research I found it would be more cost effective to buy a different car... (ive found a buyer for the vr and im saving up for a vx clubsport)