Upgrade suggestions help!

Hey guys, I've been saving up for awhile now and I'm looking to upgrade my current computer.
My budget is about £300-£400, I'm open to any suggestions.

My computer specs:

Case
ZALMAN Z11 PLUS BLACK MID TOWER CASE
Processor (CPU)
AMD FX-4170 Quad Core CPU (4.20GHz/4MB CACHE/AM3+)
Motherboard
ASUS® M5A78L-M/USB3 (M-ATX, DDR3, USB 3.0, 3Gb/s)
Memory (RAM)
8GB SAMSUNG DUAL-DDR3 1333MHz (2 X 4GB)
Graphics Card
2GB AMD RADEON™ HD7870 - DVI,HDMI,2 mDP - DX® 11, Eyefinity 4 Capable
Memory - 1st Hard Disk
1TB 3.5" SATA-III 6GB/s HDD 7200RPM 32MB CACHE
Power Supply
450W Quiet 80 PLUS Dual Rail PSU + 120mm Case Fan

You could consider the gtx 970 but your cpu is likely to bottleneck it. You could consider an ssd

What do you mean by bottleneck, should I upgrade my CPU?
What SSD should I get?

By bottleneck I mean that using a high end gpu like the gtx 970 will give lower fps than if you were using an i5 with the same gpu for more cpu bound games. You could consider a samsung or hyperx ssd

Should I just invest in a SSD and a new CPU if so what one?

I'm kinda surpassing my budget but oh well, how does this look?
http://puu.sh/gPCYV/d65fd24f85.png