Note that I don't have personal experience with either laptop, but I do have experience with the kinds of information you're using to make your decision.

I would definitely go with the Z50 here. To enumerate the pertinent specs:

• The Z50 has a better display than the G50 (1920 x 1080 vs. 1366 x 768). To put that in perspective, my (non-Retina) 13" MacBook Pro has a 1280x800 display, and it's 13". You're looking at 15" laptops.
• The Z50 can actually be cheaper than the G50, from a cursory glance at the prices (£449.95 - £499.95 vs. £499.95)
• Both have 8GB RAM, which is decent.
• The Z50 has an "SSHD", basically a 1TB HDD with an 8GB SSD on top of it. That 8GB SSD, if the software running it is built correctly (it probably is) will store your OS and most frequently used documents, improving performance drastically. The G50 doesn't have this,
• See a comparison of the processors - the G50's i7 5500U vs. the Z50's AMD FX-7500. In my opinion, the G50 actually wins out here.

However, computers, especially laptops, are almost never limited by their CPU in real-life tasks. You'll see much more benefit from that SSHD than you will from a marginally better CPU. Even as a developer, the only time I max out my processor (2.5 GHz i5) is when I'm transcoding audio with ffmpeg, or, rarely, when compiling code. In other cases, my mechanical hard drive just can't keep up, and the processor has to wait to get data from it.

Also, you mention video editing. The graphics card (AMD Radeon R7 M260DX) in the Z50 will likely win out over the G50's Intel HD 5500. I'm not an expert on graphics cards, though - see this comparison for more information.

Either of these machines would be absolute overkill for Word / Excel / PowerPoint. For video editing, I would expect the Z50 to beat out the G50.

Note that I don't have personal experience with either laptop, but I do have experience with the kinds of information you're using to make your decision.

I would definitely go with the Z50 here. To enumerate the pertinent specs:

• The Z50 has a better display than the G50 (1920 x 1080 vs. 1366 x 768). To put that in perspective, my (non-Retina) 13" MacBook Pro has a 1280x800 display, and it's 13". The 15" G50 has a lower vertical resolution than my 13" laptop, and barely beats it horizontally. Not good.
• The Z50 can actually be cheaper than the G50, from a cursory glance at the prices (£449.95 - £499.95 vs. £499.95)
• Both have 8GB RAM, which is decent.
• The Z50 has an "SSHD", basically a 1TB HDD with an 8GB SSD on top of it. That 8GB SSD, if the software running it is built correctly (it probably is) will store your OS and most frequently used documents, improving performance drastically. The G50 doesn't have this.
• See a comparison of the processors - the G50's i7 5500U vs. the Z50's AMD FX-7500. In my opinion, the G50 actually wins out here.

However, computers, especially laptops, are almost never limited by their CPU in real-life tasks. You'll see much more benefit from that SSHD than you will from a marginally better CPU. Even as a developer, the only time I max out my processor (2.5 GHz i5) is when I'm transcoding audio with ffmpeg, or, rarely, when compiling code. In other cases, my mechanical hard drive just can't keep up, and the processor has to wait to get data from it.

Also, you mention video editing. The graphics card (AMD Radeon R7 M260DX) in the Z50 will likely win out over the G50's Intel HD 5500. I'm not an expert on graphics cards, though - see this comparison for more information.

Either of these machines would be absolute overkill for Word / Excel / PowerPoint. For video editing, I would expect the Z50 to beat out the G50.