Mate, forget being realistic about price. Be strategic. The way I see it is there are 2 options you have on a private sale.
1. Price it high-ish. Its a quality motor and therefore price in the upper neck of the woods in comparison to what others are selling. the way to look at it is any potential buyer will try and knock you down on price and so it would be essential to have some room for movement. The key to this strategy is aiming for a "hook" price at which people will "bite", come view and then negotiate and leave both parties happy.
2. Price it aggressively with a base figure in mind, lowish compared to others. The key for this to work is, the potential buyer will look for faults in order to talk you down. Yet a well kept and prepped vehicle will mean he or she wouldn't be able to find any, and therefore take the car at full asking price.
I am not here to have a go at you buddy, dont see it like that, just constructive criticism. You seem like a fair chap, so assume the buyer, read bargain hunters will talk you down big time. so try to formulate a strategy ( doesn't have to be any of the above) and stick to it, dithering in between both MAY not work in your favour.
I recently sold my car (e90 330i) and also helped my friend sell his car ( r32 golf), and even this climate i feel we got top dollar if not very close to it.
and lastly I am by no means a guru, infact you could count the cars ive sold and still have fingers left on the first hand. Just be honest, and open. Obviously bare in mind its a forum and its prob better to offer some kind of discount for other members, but in terms of pistonheads and autotrader. do what you got to do.
You have a lovely car, best colour too for the e90.
All the best mate and good luck.