..... I use it on all my bikes and it's literally bomb proof. Like I said in the OP I'm looking to customise my LHT, which is why I bought a frame only. I really don't need any more 'it's not for you', thanks very much.
I'm looking for advice on most of the following:
V brakes vs minis.
Wheel combo for lightweight 26" wheels.
Tyre selection for fast, all day touring/some off road.
Potential conversion to full carbon, disc fork. (I've seen 2 forks which are virtually identical in rake ect to the stock steel)
Saddle lay back for most comfort (the LHT has a very different geo to my current steel frame)
Potential bar end handlebar mount and climbing 'blippers' to run Di2 (no STIs) see:http://carltonbale.com/shimano-di2-ever ... d-to-know/
Performance over 'rough stuff'. I'll be doing c. 500 miles of the Camino in Spain, and at least 20% is over very rough tracks
If I can get the bike down to 10.5kg (which now seems very feasible) I'd be thinking about a dropper suspension seat post, which would only cost me another 250gr.
I should say money is no object on this build! This will be my touring bike for the next ten years at least.
OK , so three pages in now and you finally tell us what you are driving at; 26" wheels....? That is important information.
I don't know whether you have offered up a modern DA chainset to a 26" wheeled LHT frame but there is a very real chance that it won't even fit without clattering the chainstay; IIRC these frames are designed to run fairly fat tyres and may well force you to run with an MTB chainline (and chainring sizes) rather than use 'road' stuff. Maybe someone with such a frame can comment on that? I'd certainly check this at a very early stage.
However my main objection to using DA chainrings for your purposes is that you will probably struggle to get the gearing low enough with the chainring sizes on offer. Gearing preference does vary but most folk who have ridden the routes you propose would specify a bottom gear in the low 20" range if not lower. You might be able to do this (using a DA chainset) with some MTB cassettes that run 40T + sprockets but this then predicates your transmission options for rear mech etc.
26" wheels and tyres have lots of choice but there are some areas where there is less than you might want. I'd always err on the side of having 36h rims and hubs (using lightweight DB spokes to keep the weight down if necessary) but there isn't so much choice in quality 36h 559 stuff. Even 32h there are not so many rims that are really good; Mavic don't seem to make a double-eyelet rim in 26" any more, and the rims they do make are not immune to cracking and seem to have rather thin braking surfaces. Rims like Sputniks are strong and have lots of meat in the braking surface, but they are a fair bit heavier.
Similarly with tyres, on a bike like that most folk would use something 40-50mm width and (even without much of a tread) such tyres will be reasonably swift on the road and ought to handle dry gravel at least. Vittoria randonneur Pro are worth looking at; some folk would choose Big Apples... maybe there are some more options that are worth thinking of.
If you go to a front disc brake that is one less rim to worry about wearing out, but.... you may struggle to find a fork with a sufficiently low crown height that won't 'modify' the steering geometry (out to about 70.5 degrees head angle or something). Most carbon disc forks are meant for 700C and if they have room for fat tyres they have crown heights that are perhaps a bit taller than fits perfectly on your frame....? [ Surly say 376mm 'fork length' for 26" LHT frames vs 390mm length for 700C wheeled LHT frames]. Maybe someone knows of a suitable fork for you but I don't imagine it is a commonplace item.
For brakes a simple option is to use a V at the back, a V (or MTB cable disc) at the front, and V-pull brake levers for dropped bars. I suspect that if you try to use Mini-Vs with mudguards on that frame, you may need to drop the mudguards below the fork crown/brake bridge in order to get enough clearance between the brake and the mudguard. This could in turn limit tyre choice and/or mudguard clearance.
You can (with application of enough time, effort, and money) build almost anything. But I think if you left a dozen different people with your frame, a mission to build a bike for the purpose you intend and a warehouse full of bike components, you might come up with a dozen different bikes, none of which are quite like the one you envisage. 'Fast on the road' means a lot of different things to a lot of different people. I've built quite a few touring oriented bikes with 26" wheels and they have varied from something that was like a 'rigid race MTB with slicks and dropped bars' to something altogether more tank-like. I shall be interested to see how yours turns out!