Presently on i5 4670 oc 4.0ghz considering upgrade to skylake is it worth it . 970 graphics card at moment running prepar3d as sim . If its woth the upgrade do i need to spend the extra £120 on the i7 6700 . Anyone any experience yet.

Depends on how much performance you currently experience and how much you're willing to spend to have more.  Realistically, you need to spend somewhere around $500-600 on a platform upgrade.  You can't just drop a Skylake CPU into your current motherboard, they don't use the same socket.  You also would need to purchase different RAM since Skylake uses DDR4.  If you're on a budget, it's not worth it.  You should overclock your current chip further.  4GHz is barely an overclock for a 4670k.  

I would if any good at o/c have good cooling fan and  have only used gigabytes ez tune feature . found little difference between 4 and 4.4ghz apart from my cpu runs hotter 60-70 instead of high 40s on 4 .did not get the gain to warrant it. 3-4fps max  on high scenary and complex airliners.i have gigabyte z87 hd3 mb no good guides for these .running an evga 970 not sli 3 monitors . need to change mb to go sli .£550  in uk for upgrade to sli and skylake processor plus ram may get a couple of hundred selling old parts on ebay. another graphics card when funds allow.

What kind of performance are you getting now?

 

It's pretty much what Techguy said.

Not particularly bad most of the time sometimes exceptional egll heathrow aerosoft  737 pdmg no traffic no weather moderate settings on prep3d 15fps in vc depending where in airport but this is worst case.

I would if any good at o/c have good cooling fan and  have only used gigabytes ez tune feature . found little difference between 4 and 4.4ghz apart from my cpu runs hotter 60-70 instead of high 40s on 4 .did not get the gain to warrant it. 3-4fps max  on high scenary and complex airliners.i have gigabyte z87 hd3 mb no good guides for these .running an evga 970 not sli 3 monitors . need to change mb to go sli .£550  in uk for upgrade to sli and skylake processor plus ram may get a couple of hundred selling old parts on ebay. another graphics card when funds allow.

 

4.4GHz on Haswell is just scratching the surface.  4.6GHz is likely within the reach of any chip as long as you have decent cooling.  4.7-4.8GHz is possible, and 4.9-5.0GHz is not unheard of.  I myself run a 4790k @ 5.0GHz with voltage headroom to spare.  

 

Not particularly bad most of the time sometimes exceptional egll heathrow aerosoft  737 pdmg no traffic no weather moderate settings on prep3d 15fps in vc depending where in airport but this is worst case.

 

You mentioned a 3-4FPS boost by overclocking from 4GHz to 4.4GHz.  If you're getting 15FPS @ 4GHz, that should mean you're at 18-19FPS @ 4.4GHz.  If you can get 4.6GHz, and bump up your RAM speed a bit, 20+ FPS should be possible and going from 15 to 20 FPS in FS can be the difference between a noticeable stutter and smooth flying.  

thx techguy will look in to this . Still much to learn on overclocking can you recommend a good idiot guide all the ones I have read are far to detailed

Sorry overclocking makes little difference on my sys back where I started at 4ghz nice , stable and cool  and just as quick . if not more ,Overclocking for those with patience and knowhow .

I guarantee you overclocking makes a difference.  I'll bet my FSXMark 11 score is at least 25% higher than yours and we both run Haswell chips.  When things get rough, that extra 25% could be the difference between stuttering and unflyable vs. smooth enough to let you operate.  

Sorry overclocking makes little difference on my sys back where I started at 4ghz nice , stable and cool  and just as quick . if not more ,Overclocking for those with patience and knowhow .

If you didnt benefit from a moderate OC and Im guessing you got to 4.5ghz? and there was no change in your system then its unlikely skylake will help much. P3D is GPU intensive so your probably better off upgrading your 970 to a 980ti