once you're willing to go to 45m, an extra 5m is not going to make a difference. he's not going to have less pressure on him at 45m vs 50m. if he fails to bring his 2012/13 form to arsenal he won't be looked at as less of a failure if his fee was 45m instead of 50m. i'd probably say the same thing for 40m vs 50m. you have to get your man at that point.
i personally wouldn't go for his racist ass past 30m (since they seem determined to buy the cvnt), but his value is his value.