I did a lot of research into this a couple of years ago (as Shrek will attest as he was one of the people who helped shape my final decision).
The V8 4.2 is a glorious car in terms of it's theatrics, the sound of the engine, the effortless power delivery, the comfort and the looks all come together to deliver a beguiling and compelling car. However all that glitters is not always gold, so these are my personal views on why I went away, saved up and went for the facelift model 3.0V6T.
1. The V8 is thirsty, even more so than the V6. Expect MPG's with a 1 at the front around town (e.g. 18, not 118!), and flat out driving at the lower end of the teens. Average day to day if you hit 25 you're a better person than I am, so it's greedy
2. The sound is glorious, but unless you have the wallet (and taste) of Cuppa the sound tends to sound bigger than the power that it delivers. It's so linear that it doesn't feel fast IF you come from a perky turbocharged performance hatch. If you've come from smaller engined cars then it will be fine.
3. Tuning potential (not important to everyone). I worked out the other day if you wanted to achieve maximum bang per buck you could go to MRC in Banbury and get (approx) 480bhp from the 3.0V6T for £1700. That's about 130bhp increase for less than £2k. If you spent £2k on engine mods for the V8 I think you'd be lucky to see 30bhp. You need a supercharger conversion on the V8 to make it a properly quick car, and this is the only route to do this and you're looking at £10k and some evasive modding.
4. Carbon fouling from FSi. I've seen quite a few threads from V8 owners cross platforms with early onset carbonation issues in the valves that have had to be cleaned up. It can cause rough idle, power loss and it will depend on servicing regime and type of driving as to how quickly this build up. There isn't enough evidence as it's newer on the 3.0V6T as to whether it suffers similarly.
5. Manual gearbox. Personally I prefer a manual, but I've read quite a few threads outlining issues with pedal vibration and clutch related issues so if you test drive any cars keep this in mind.
There are still positives for the pre-facelift though, some will always prefer the bigger capacity lump, the prefacelift 'bull' lights and looks, and the hydraulic steering (rather than the slightly unusual electro-mechanical steering on the facelift). The facelift wasn't just a cosmetic change, it was a mid life enhancement with revisions to the suspension set up, crown diff, and the tech capabilities of the car internally were improved (bluetooth streaming / Nav with Google / multi sim / hi-def screen with 7 digit postcode nav etc.)
As with any car, many of the faults and niggles get engineered out over it's lifetime, so I have found on three different models of cars that the later cars seem to be slightly more polished, but that's just a personal view. Whatever you buy, choose carefully, and ensure the car comes with some sort of warranty as if you're doing it out of love rather than an expansive wallet these cars could bite hard (either!).
