New to road cycling! Any recommendations for first bike? 6ft 4" budget up to £1000 ideally £600-£750

All the bikes you have listed look good for the money. The Canyon Roadlite AL 6.0 has a better groupset (Shimano 105 gears and brakes) and better wheels and tyres than any of them. It would be well worth a look for £869. A friend of mine has one and he says that it's great.

If you want a bike fitting, expert advice and a choice of every component then go to Condor Cycles on Grays Inn Road.
It will cost you a bit more than your budget but you'll be getting something that's just right for you.

Just bought the Merckx. I know there might not be many reviews about the around so i thought i would post something. Since it literally came today i've only got the test ride to talk about it but i thought it was a great bike with a very nice ride and the 30 minute test ride i had felt more like 3 minutes. TBH, like advice above one of the best things you could do is to go to a bike shop, talk to them (or knowledgeable friends you might know) and test ride as many bikes as you can. Remember with Merckx, the sizing is a tad funny so just because you are a certain size on specailized, doesnt mean you are the same on Eddy. Finally, Tiagra at £700 is a steal. Hope i've helped.

Just come back from a VIP night at Leisure Lake Bikes in Daventry..
They had a rep from Mekk and 5 bikes.
Look exceptional in the flesh and well equipped for the price

Have a play with the Ribble Cycles bike builder

http://www.ribblecycles.co.uk/pu/road-track-bike/bike-builder/bikebuilder/1

or check out their Special editions

http://www.ribblecycles.co.uk/pu/road-track-bike/special-edition-bikes/s...

I was dubious about parting with my wedge for an R782 unridden, but had chance to ride a De Rosa R838 and that's fairly similar.

Sportive Bianco is a good value bike, too.

Don't discount Canyon also - some great sub £1K bikes on their online shop

I've ridden an Allez for the past 3 years, its been great. I've upgraded the groupset from Sora to 105 as things have worn out and fitted a new set of wheels which made a big difference but the stock bike was fine to begin with.
I use this bike in the wet weather only so its had to put up with a lot of crud and has performed really well.

I'm a knuckle-dragger as well, but don't dispair there are off-the-shelf bikes that fit. A bike to commute on will have different preferences compared to training/sportives/racing. Getting the correct seat position, maybe a seatpost with some 'layback' and a handlebar post slightly longer than standard will add to your comfort. Also check the crank lengths in the bike you are being offered if your legs make up a lot of your 6'4".
You have lots of great bike shops in London, and some of the larger chains have good reputations and opportunity to test-ride as well - so no excuse for buying online and the local shop will help with servicing etc.
A 1k budget is a great price point to be shopping at!

I would suggest you visit more than one shop. That way you get a good wider of bikes to choose from and to see the range of recommendations and also the attitude of the staff in each.

Some still have a condescending attitude to customers who don't know their tubs from their clinchers whereas others are smarter and value their customers, regardless of whether they are spending £5,000 or just £5.

If you have a shortlist and want some input then we may have some suggestions but TBH you can probably find a bike that fits you and feels and looks 'right' to you. After all, it's you that will be riding it.

It all depends on what you want your bike for and what you plan to do on it in the future. A bit cryptic I know but it has a huge bearing on which type of bike to get. Going to a local bike shop and having a chat with them about what you'd like from the bike would be a good first step