Quote Originally Posted by nige
I just went and test drove this....

http://www.carzone.ie/search/BMW/6-Series/635d-Spo/117614181052137670/advert?channel=CARS

in Frank Keane BMW on the Naas Road. Its a very very nice car, looks far better in the flesh. It seems to be at the top end of the market in terms of price. I sat down and did the numbers with him and I'm in 2 minds now with what to do. It could be bought for 30k, but I'm not sure if there's any value in it? 2 owner car, 106km, full history and a 2 year warranty.

Decisions, decisions. I hopped straight out of the M3 and into it. Far superior cabin and it looks beautiful in the flesh, capable in terms of power, but i was a little underwhelmed. Im assuming you really feel the benefit of the grunt while up and running?
The only advantage the the 635d has over your M3 is that its a more modern car with the enhanced cabin and gadgets that come with the more modern technology.
If you have a good E46 M3 then financially that car will stand by you better than that 635d which is could still drop a fair few thousand in value over the next few years.
The total running cost of that E63 compared to the M3 would likely be very similar.

Given the current price of fuel I personally would go for a 650i if I was in the market for a E63.