2 x 6950 OR 1 x R9 280x

[G K G]

I already have 2x r9-280s(each gives me a average of 720kh/s)-running on a 850w and i'm planning to add 1 more. And also, i already have an extra 750w PSU and also 3 more empty pci-e slots (1x)
So i though instead of 1 x R9-280x, why not buy 2 x 6950s.

2 x 6950 - $380 ($190 each -  Powercolor 2GB DDR5)
1 x R9-280 - $430 (sapphire vapor x)

from the litecoin hardware comparison page i assume each 6950 will give ~480kh/s, so both together will give ~960kh/s. so i''l have ~250kh/s extra (with double the power consumption, of-course).

So i'll pay $50 less for the hardware and get 35% more hashes(+250kh/s), but will have to pay $11 extra in monthly electricity bill(i live in india)

Anybody have some suggestions on this?

[sitefive]

dont buy powercolor cards! worst crap ever.. and you can Flash only certain 6950 cards to 6970 in order to run them at that 480 otherwise they will be max 420khs.( and I doubt powercolor would even achieve that)
and a good r9 280x can run at 800khs overclocked.

[G K G]

dont buy powercolor cards! worst crap ever.. and you can Flash only certain 6950 cards to 6970 in order to run them at that 480 otherwise they will be max 420khs.( and I doubt powercolor would even achieve that)
and a good r9 280x can run at 800khs overclocked.

But my r9-280x gives only a max of 750kh/s even when overclocked, but they give only 720 -730 stable

And about the 6950. are you sure these cards couldn't e flashed.. i was hoping it would