Is a custom road frame worthwhile? I've been riding a Marin San Anselmo hybrid for some 13 years and I'd guess I've done over 7000 miles on it almost exclusively on the road (and it's not my commuting bike).

I'm gradually doing more cycling and longer distances and I'm finding myself increasingly uncomfortable (neck and inside leg). So I'm starting to wonder if it's actually suited to the kind of riding I do. I'm already looking to get a proper bike fit, but I'm also considering a custom frame in steel or titanium with higher spec components and (gulp!) drop handlebars.

I'm 5ft 8in (174cm), 30inch inside leg, 10 stone (140lbs/64kg). A bit small for a bloke, but not that freaky for a cyclist perhaps!

At the level of bike I'm looking at, the cost doesn't seem to be much more than something off the shelf, but it is a lot more hassle. Then again I hope this bike to last me the rest of my days, so maybe it's worth the effort to get it right.

So I'm wondering if a custom frame will make me more comfortable and/or faster and what experiences similar-sized people have had.
As a cyclist who had a hard time getting comfortable on road geometry with drop handlebars, I will recommend that you ride as many different bikes as possible for a long time before you consider dropping money on a "custom" bike.

Considering frame material and construction, geometry quirks, wheel sizes, brake types, drivetrain compatibility, tire clearance, frame lifespan, braze-ons, so on and so forth....there are LOTS of different bikes out there. To illustrate this, consider: 


A lugged steel touring bike with 650b wheels, cantilever brakes, ample tire clearance, and brazed-on fittings for racks, pumps, bottles and whatnot
A carbon fiber race bike with integrated headset/bottom bracket, tucked in rear wheel, seat mast, 700c wheels with aero-spokes, etc. etc.


These bikes are two very different creatures. You can find shops who can fit you to either with great aplomb, but in reality these bikes are not interchangeable (regardless of whether you think one is better than the other.) The issue is less of fitting a bike to a person's body parts, and more of fitting it to a person's needs and wants. 

You're just about my size, maybe an inch shorter, and I usually ride a 56 cm frame - a very common frame size. Being an average size (yes, you are an average size guy) you essentially have the bike world at your disposal. 

Some people may feel like a "lifetime" bike exists for them, but I'm of the opinion that there is no need to be wedded to a bicycle because they are so very diverse - bicycles fill more of a use than fitting your body properly (and the inescapable truth is that your body will change just as surely as your cycling needs will.)

My short recommendation is to invest in a good-fitting touring or sport-touring bike with a steel frame. They're comfortable, versatile, affordable, long-living, and easy to service. It'll be way easier to get comfortable on this than an aggressive road bike and it will also be easier to sell down the road (because touring components use pretty much the same technology now as over the last 25-40 years.)