How much power does a 6870 use?

Two 5770s will pull a maximum of 216 watts at full load, 108 watts for each card. A single 6870 will pull a maximum of 168 watts at full load. You would get roughly similar performance and would get lower power consumption with the single 6870 over the two 5770s. However the power savings is 48 watts rather than the 108 you save using one 5770 rather than two, you will want to make sure you house's electrical system can even handle a 168 watt card before buying.

Are there any other cards that have close to the same performance as the 6870, but uses closer to the 108 watts? like below 130, as i don't know how much the house can handle. Unless i just stick to the one 5770 till i move.

Unfortunately around that performance bracket, most cards are quite power hungry. The Radeon HD 5850 has similar performance to the 6870 outside of DX11 and pulls a maximum of 150 watts. The slightly slower 6850 pulls a maximum of slightly less than 150 watts. Nvidia's cards tend to be more power hungry, the GTX 460 1GB, about equivalent to a 6850 pulls a maximum of 180 watts. I think the GTX 560 also pulls a similar amount of power.

There's nothing beneath a 130 watt maximum that would get you similar performance. According to a recent power consumption benchmark in the graphics card guide article, a 6850 did seem to only pull 125 watts when running the Perlin Noise benchmark utility, however there is no guarantee that it won't exceed 130 watts at load, the maximum for the 6850 is somewhere in the 140s I believe.

What are the rest of the things in your system and what power supply do you have? If its an older less efficient one, particularly one with passive or no PFC it boosts your chances to flip the breaker. While graphics are one of the most power intensive parts of a system, 2 5770s in a system shouldnt be pulling more than 350W from the PSU, which on a modern unit would be less than 440W from the wall which is well below the limit for any breaker.

Well the house hasn't been rewired in like 40yrs lmao so it could be lower than 440w, but i'm running a older psu, i bought with my first older build. It's a rosewill rp600v2-s-sl, few weeks back i upgraded to a 2500k though and it's oc'd to 4.3ghz

An i5 2500K at that level ups the power consumption figure i had a fair amount, i would put it closer to 450W from the PSU in that case(i was figuring a little 95W CPU, not an OCed one with a good board etc). That rosewill says >72% efficiency on its newegg page so lets assume that for worst case scenario.

450W DC at 72% efficiency is 625W AC from the wall, assuming you are on 115V power, thats about 5.4 amps of current, it also says no PFC which means that its power factor at full load may be as low as 0.55 according to the jonnyguru FAQs on PFC. That puts the complex current pulled from the wall at 5.4/0.55=9.82A, close enough that if you are on a 10 Amp circuit it could trip the breaker, if you move to a unit with good efficiency and active PFC you will be able to use a lot more real power.

So i should just stick with the 5770 till i move then? as it doesn't seem like it'll be able to handle anything more powerful thats really worth an upgrade.

You could get a more efficient power supply, or ditch the overclock on the i5 2500k so you would have more power available to run both 5770s. You really don't need the overclock anyway. At stock clocks an i5 2500k can handle two 5770s quite easily.

I'll give it a try with the stock clock again, but i think it'd still be to much power with the two 5770's.

216w blows your home breaker?? How do you cook, use a/c, run a hot water heater, blow dryer, etc??

Just a clothes dryer alone uses 6000w.