New R9 280X doesn't seem up to par, power issues?

Yesterday I got to replace my GTX 750 with a new (well open box) XFX Double D R9 280X. However since I've put the card in I've had nothing but issues, and i'm wondering if it might be my PSU. The card doesn't seem to be performing newarly as well as it should in games or benchmarks, and in one game (Interstellar Marines) my little 750 actually outperforms it at times (with a steady 20-30 FPS compared to the R9's 25-40 on the same settings). In the firestrike benchmark as well, it only performs a bit better than said 750. Some games (Like Payday 2) are still running just fine but it just seems like they should be a lot better. I also have F1 2014 and I can't pull anywhere above 30FPS on anything but the lowest settings. I have:

Made sure I had the most recent driver
Rolled back said driver and let AMD install the one they recommend (14.12 without dotnet for Windows 8.1 x64)
Checked GPU-Z to make sure the clock is running at 1000MHz and memory at 1500MHz
Checked the Catalyst Control Center for these two things. CCC also lists the power at 0%, even under load.

One other thing I had to do was change how I was powering the card. My PSU has one PCIe power coming off and also came with a cable (because it is modular) to turn that one into 2. The R9's manual says not to do that, so I have the 8pin power coming from the PSU's PCIe power cable and the 6pin from two MOLEX connectors.

This is a fairly new install of Windows 8.1 x64, all the drivers are taken care of, chipset drivers etc, and I'll list my specs below.

Motherboard: Asrock H87 Pro4
CPU: Intel i5 4430 @ 3.00Ghz (3.3 Turbo)
Memory: GSkill Ripjaws 8GB (2x4) 1333 MHz (OC'd to 1600)
GPU: XFX R9 280X Double D. 2048 stream processors, 1000MHz core clock, 1500 mem clock
SSD: 256GB ADATA Sx900 series
PSU: Raidmax RS 730SS 730W a picture of the wattage table (?) is included in pictures




Monitor is an HP monitor @ 1600x900 and 60Hz refresh

Firestrike score with GTX 750: 3345
Firestrike score with R9 280X: 3940 (This is the second time. The first time it was 4940 but my games still didn't run well. 3940 is the second test after fixing the power setup). I just feel like the card should be performing so much better. Included are pictures of the GPUZ and CCC while it is under load (Payday 2: 1600x900, no VSYNC, max detail and textures, 16xMSAA), and the PSU's power table thing.

I have no idea what could be going on and it's frustrating me that the card would perform like this, practically in the same class as a GTX 750. Can someone please tell me what might be going on?

Update: I switched out the Raidmax with the Rosewill from another computer and it's performing much better, and is at least playable until I can buy a replacement for the Rosewill. I see that it has 38A on the 12v Rail, what should I be shooting for?