I would send them the exact same offer.
Here's why:
1) Your offer of $425,000 is 65% of what the home is currently worth. If it needs 200k of work to be worth 850k, then it is reasonable to assume that the actual value of the home is 650k. Obviously as an investor you want to buy at a price where you can make a profit. (which is reflective of your offer of $425k).
$425k + $200k = 625k
625/850 = .74
Your all in cost 74% of retail value. If you sell with an agent charging 5% commission, you can deduct 42,500 from your sales price. Putting your profit around $182,500 less holding costs.
Also, the bank has already setup an auction and taken bids etc etc. Costing them more money that they're getting negative returns on.
Finally, with them already having had an auction, and you winning with the bid of $425k.... it would be irrational for them to hold another auction in the hopes that hey get a higher bid. Sure, it could happen, but they have to be thinking, "what if it doesn't? Can we go back to @Sam Mathew and ask if his offer of $425k is still on the table?" Hell no. Now the offer is at 375k. Right?
Too make a long story short, I think your offer of $425k is reasonable, and the bank doesn't have any leverage to negotiate.
Good luck!! keep us updated :)