I have 2 R9 290s,mining grin one does 2.5Gps, another does 2.77, I'll be trying to figure that out later. It's lower power than eth, but I'm not sure by how much as my kill-a-watt is dead. It will work on linux (tested with SMOS myself), it might work on windows 7, but not windows 10. On Linux you can get 27-31MH/s on ethash (vs the 20-24 on windows) too. My experience mining cryptonight variants on my 290s has been.. well I'm only getting 700 or so H/s. Grin was definitely making me more profit, and eth classic making the most revenue and maybe profit. You need to use Hawaii Bios Editor to do any overclocking/undervolting you want if using them on linux.
edit: lolminer is miner to use for grin on AMD.
edit2: Less typical or efficient algos the 290s can do are: the equihash variants, like zhash, BEAM, and I believe Aion but I didn't test that one myself. I believe mine were outperforming my RX 580 on BEAM, too, but I've only tested on linux. Windows 7 may work the same even though it doesn't get the memory management benefits of linux, where the ethash performance difference comes from. They can do the C31 algo, for grin, as well with lolminer but only at .27 gps, though they ran fairly cool when mining that so power efficiency may be better there.