How do you figure that? How many hashes per 5870 and what price are you getting them at?
$280 5870, 460MH/s = 1.64 MH/$
$400 5970, 700MH/s = 1.75 MH/$
Unless you are finding 5870 at less than $250 per card new I don't see how they are best hasher per $$$.
Are far as the 5970s being "silly money" unless you are only buying one card, 2x 5870 cost more than a 5970.
5970 makes deployment simpler and has higher electrical efficiency. However keep buying those 5870s I don't want the price to go up on 5970s.
Trust me mate. Here in the UK we get foked over by the gov. The prices are insane here. 2x5870 much cheaper than a 5970. 400 USD for 5970 is MAGIC to us.
Not to mention the cost of electricity... anyway, when was the last time you saw a 5850 or 5870 on a UK website (new, not overclocked till the original owner smelled smoke and returned it under distance selling regulations
) - let alone for sensible money?
Remember, manufacturers are *still* turning out new designs of cards using the 5830 cores - I spotted a load for sale on videocardshop.co.uk and picked some up, thinking they'd be the same 'Value' 5830 (made by Peak, with two protruding tall heatpipes, every one with snapped fan housing screws, though that didn't stop them working, and all with completely random overclocking potential from extreme to limited).
They weren't - they were new XFX units - a completely new design I hadn't seen before, no complete card shroud, just a spiral-heatpipe fan cooler and a passive heatsink on the VRMs. I haven't tried overclocking these in anger yet, but the one I've got up and running seems OK (around 5˚C hotter than the Peak twin-heatpipe shrouded cards, at 850/300 and around 275 MH/sec).
I presume that all the Cypress cards (5830, 5850, 5870) are effectively the same chip but graded according to defects, right? Or are they specifically designed differently? Seems odd that there's still a supply of *new* Cypress silicon into the market - there's obviously demand because the 5830 is pretty decent in terms of hash per watt in bitcoin mining, but if these new XFX designs aren't just using up surplus production, and AMD are still running Cypress chips on their fabs, then we may be waiting longer for the 78xx cards than expected.
IMO, I'd be happy with identical hashing performance but half the power consumption. In the UK, electricity is the main cost for heavy bitcoin mining...