As I'm testing my new appraisal system, I punched this in and got this:
videogames.ag $1837.60
If you have a sure sale at $750 and need the money, take it (assuming you actually profit). If you can afford to hold on / negotiate, might as well aim for the above figure or at least towards it. As always, a guaranteed sale is very valuable and often worth bringing the price down a bit - you never know when you get the next offer especially this being an .ag - even though the keywords are golden.
I have some experience in regretting not letting a name go. I got mid $xxx offers for a couple of my names but did not sell - it's been very quiet ever since and I could have bought a much nicer name with the combined profits...