Still...what can I do now?
add 5k more to test the waters? (I have nothing to lose) I think I can put int 10k more. There are other houses around in the market but I like this one because it's close.
Or is this my last chance: a 'win it or lose it' moment?
If you offer $10K more now and they accept it, you may wonder whether they would have accepted $5K less than you offered. I don't know. Does it matter? You'll have the security of knowing it's yours, at a price you can live with, and I bet you'll never think about it again after you've started organising settlement, if you're excited about having the property. (If it's an investment, you need to be more hard-nosed about it and I'd tend to only offer $5K more, initially.)
If you offer only $5K more, you can still make a further offer if they reject that, too, but you run the risk that somebody else offers $8K or $10K more in the meanwhile, and that other bidder secures the property at a price that you were willing to pay.
Would that hurt more than wondering whether you'd paid $5K too much? If I really wanted this house as a PPOR, it would hurt a whole lot more to miss out.
But I don't know how much you want this house, whether there are other houses out there that you'll love, or whether this one is something rare / unique. Also, if the market's moving, you may end up paying more by waiting.
Only you can weigh all those factors up with your own psychology...
Edit: Of course, there's also a chance you'll offer $10K more and they'll still reject the offer, in which case you can't afford it and you can get looking for your next option more quickly.