you could up your raw cpu power by jumping to socket 1150 or even 1151.
but it would mean a £300-350 spend. you would literally double your cpu performance for things like editing.
wont do a lot for gaming but video editing would benefit from the faster cpu, ram and bus speeds.
from what i can find the max spec cpu is the q6600 on that board
the motherboard will take a max of 8 gig of ram.
the psu is a 300w standard unit...
you could go a budget rout and get an amd 8 core 8gig ddr3 1600-2133 and get very good video editing performance.
PCPartPicker part list:
http://uk.pcpartpicker.com/p/L7bqjX
Price breakdown by merchant:
http://uk.pcpartpicker.com/p/L7bqjX/by_merchant/
CPU: AMD FX-8350 4.0GHz 8-Core Processor (£129.95 @ Amazon UK)
Motherboard: ASRock 980DE3/U3S3 ATX AM3+ Motherboard (£46.84 @ More Computers)
Memory: Kingston HyperX FURY 8GB (2 x 4GB) DDR3-1600 Memory (£32.62 @ Ebuyer)
Power Supply: SeaSonic ECO 430W 80+ Bronze Certified Fully-Modular ATX Power Supply (£34.98 @ Amazon UK)
Total: £244.39
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-12-05 23:36 GMT+0000
about £275 if you go with 16 gigs of 2133
if you wanna go the intel rout.
then any i5 quadcore (k series) 8-16 gig ddr3 1600-1866 with an oc enabled motherboard. for about 325
PCPartPicker part list:
http://uk.pcpartpicker.com/p/k4Wxpg
Price breakdown by merchant:
http://uk.pcpartpicker.com/p/k4Wxpg/by_merchant/
CPU: Intel Core i5-6600 3.3GHz Quad-Core Processor (£155.00 @ Amazon UK)
Motherboard: Asus Z170-P D3 ATX LGA1151 Motherboard (£78.56 @ Amazon UK)
Memory: Kingston HyperX Fury Black 8GB (2 x 4GB) DDR3-1866 Memory (£33.96 @ More Computers)
Power Supply: Super Flower Golden Green HX 550W 80+ Gold Certified ATX Power Supply (£57.12 @ CCL Computers)
Total: £324.64
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-12-05 23:48 GMT+0000
honestly i wouldnt bother putting an ssd in a 775 build. due to the older sata/pci-e standards mean limited bandwidth and limited compatability.
the ssd gains would be minimal over a hdd, and could cause bottlenecking on read writes across disks. due to being sata 2
anyhoo, just opinions. personally i would go with the intel build. although the amd isnt far off and costs a fair bit less.
gpu compatibility on your current motherboard may be an issue if it has a 1.0a pci-e slot. pci-e 2 wasnt completely compatible with it. so a lot of pci-e 2+ cards dont work with the earlier standard. if the pci-e is 1.1 then you should be fine.
max recommended would probably be a 750ti or equivalent amd and a 350w minimum psu, 450w preferred.