The 4.3's aren't as good to drive as the 4.7's, they are very much underpowered when compared to a 911, the 4.7 was released in order to bring the Vantage back into the same playing field as the Porsche.
With regards to running costs, expect it to be expensive, it does depend on how you are going to get it serviced, I would expect you will take it to a dealer or at least a specialist in order to keep a FSH. They are not cheap on bits or labour. If you do get one, I suggest you get the warranty from AML as they cover almost everything. All parts not covered by the warranty wil be main dealer only, the amount of work that goes into the components, such as tyres and pads is unbelievable, the tyres are specially made for the car and cost around 3-400 pound each.
If you do get one, find the largest dealer you can for any work or bits, as they get the biggest discount so pass it on to the end user.
If you could find the extra money, I'd go for the DB9, the 6.0 V12 is outstanding. The DBS is even better, but the initial cost and running costs for those is beyond belief, they are for the seriously rich only - think approximately 2-3 thousand pound for one brake disc!