Also have a look at this:
http://www.anandtech.com/bench/Product/399?vs=406
Since they don't have 3870K, would use the 3850 is as it is close enough (3.00GHz vs 2.90GHz). To compensation for the 100MHz slower, for Intel side would use a G620 (200MHz slower) instead of a G840 (2.60GHz vs 2.80GHz).
WOW average frame rate:
3850: 68.8fps
G620: 83fps
So you can pretty much bet on the minimum frame rate that the Llano would be somewhere around 10fps lower than the Pentium, which is make or break on the difference between 20fps and 30fps~. 20fps is by far rougher than 30fps in terms of smoothness for eyes preception.
Too many but this but that, but people fail to give good reasoning why the 3870K is better for OP's, except it can be...well *may be* £10 cheaper...despite the Pentium+6670 combo would do better on
what the OP use it for and
within his expected budget?
And seriously...people that dismiss future upgrade as pointless shouldn't be giving people advise at all. Who are they to dictate people not to upgrade their PC? Can probably pick up a 2nd hand Sandy/Ivy i5 for £50-£60 is couple years time, whereas getting a shiny new platform upgrade would cost around £300.