Don't be so mean guys I'm just newbie to the whole mining thing just saw somewhere on aliexpress ltc miners and I thought they can mine all scrypt currencies... so I guess I need to build gpu rig ... thank you for the replies..
They can - but Ethereum isn't a scrypt-based coin.
Don't need to flash a R9 290 to R9 290x (which doesn't work very often, seems like the only ones it ever worked on were some VERY EARLY R9 290s - but can't hurt to try) to get good ETH hashrate.
Flash with one of the modded bios by TheStilt, should be able to run at 1100/1250 at that point as long as the ambient isn't way high, good for about 28 Mh/s right now.
I'm pretty sure that those modded bios only work on reference-board models, but that's a lot of the R9 290s out there.
He also made versions for the R9 290x - could try one of those first, nice thing about the R9 290 is that I'm pretty sure they're all "dual bios" so if you brick one bios you can use the other to get the card back.
I have no clue what they would do on dual mining, never bothered trying it.