The 860 is more powerful, but in the end it'll probably be out of your pricepoint. Either way there's always something more powerful, so you'll eventually have to settle for something. The 850 will easily max out Civ 6 and most other modern games, and it should be able to play games on at least medium for another three years or so. 

Yeah, at this point pretty much no game uses 8gb of RAM. Heck, most don't even use 4. 

SSDs are nice, I have one in my desktop, but they aren't necessary. I personally don't have one in my laptop because laptop SSDs tend to be obscenely expensive overall. The boot time will be slower, but Windows 8 isn't that resource-intensive so it won't be that bad at all, maybe three or four minutes to boot up completely. As long as you simply put it into sleep mode instead of turning it off, you probably won't even notice that you don't have an SSD.

Yes its always tricky.

On the one hand, I will keep the laptop a minimum of three years (and I look after my tech), so I am tempted by the extra power of the 860, and the extra convenience of an SDD. The RAM on the other hand, I can likely upgrade later with an 8GB stick if I ever need too right?

*decisions*

Correct. You can always upgrade your RAM for relatively cheap if you so wish.

From what I see, neither the 850 nor the 860 are quite future-proof aftwr three years. No mobile graphocs card really is. I personally have a 750m in my laptop, and it plays most gamea just as well as the 7970 in my desktop.

If you really want to be safe, that 860 may be a better option, but if its out of your pricepoint I wouldn't sweat it. The 850 will do just fine.

I wouldnt worry bout the SSD. Just get one later on for cheaper and put it in there if you so wish.

Went WAY overboard in the end:

Standard Metabox Design
15.6" FHD (1920 x 1080) LED Matte
Nvidia GeForce GTX 860M with 2GB GDDR5 VRAM
Intel Core i7-4710MQ Processor (6M Cache up to 3.50 GHz)
16GB 1600MHZ Memory
Plextor 256GB M5 PRO XTREME SATA3 SSD
1TB 7200RPM HDD
802.11ABGN / Bluetooth
Blu-ray Reader / DVD +- R/RW DL
Windows 8.1 64BIT
2 Year Platinum Metabox Onsite Pickup

I really wanted to sub out the Blu-Ray player for a 95% Matte Gamut screen but that was a degree of customisation they couldn't do without adding hundreds to the (~1700) price.

The RAM was a free upgrade from 8 to 16 so I was like fine.

Here is hoping its awesome!

That sounds like a beastly laptop! You'll be golden for years to come, congrats!

Haha yes, but I wont be able to afford games for years to come

Fortunately my Steam backlog is enormous, so I'll just have to port my account to the new Laptop ASAP and get cracking!

Went WAY overboard in the end:

Standard Metabox Design
15.6" FHD (1920 x 1080) LED Matte
Nvidia GeForce GTX 860M with 2GB GDDR5 VRAM
Intel Core i7-4710MQ Processor (6M Cache up to 3.50 GHz)
16GB 1600MHZ Memory
Plextor 256GB M5 PRO XTREME SATA3 SSD
1TB 7200RPM HDD
802.11ABGN / Bluetooth
Blu-ray Reader / DVD +- R/RW DL
Windows 8.1 64BIT
2 Year Platinum Metabox Onsite Pickup

I really wanted to sub out the Blu-Ray player for a 95% Matte Gamut screen but that was a degree of customisation they couldn't do without adding hundreds to the (~1700) price.

The RAM was a free upgrade from 8 to 16 so I was like fine.

Here is hoping its awesome!

god i know that feeling all too well,  i do a lot of travelling for work and wanted something beefier to play some games in my downtime rather than being bored in airports and hotels,  ended up buying a eurocom x7 and spending twice my initial budget

final specs for it are as shown : http://i.imgur.com/qK7kyrI.png

plays absolutely beautifully though,  and i havent regretted the spend even once,  you'll feel the same way when you throw a modern game at it and it playa it smooth as silk,  theres something about a laptop spitting out smooth high end graphics that has a weird air of awesomeness about it.