Actually, I've been working on that very comparison myself, from an even older time - I've been comparing a 30 year old racer to a contemporary cycle. So far, it's just been a few rides on the old bike (just bought it), and the comparison is turning out to be quite interesting.
Recently, I bought a 1970's vintage Falcon San Remo 76, a classic high end British cycle of that era: All Campy NR, Reynolds 531 frame with Campy dropouts, Brooks Team Pro saddle, Cinelli bars, Campy hi flange Record hubs with 3 cross spoke lacing. Only nod to contemporary cycling is the replacement of the old Weinmann tubular rims with Mavic clinchers - current clinchers are about as good as tubulars of that era, and quite a bit more practical. I got this bike recently because it's what I used to ride in college.
It's an interesting contrast with my current road bike - Trek Y-Foil, carbon aero beam frame with Campy Chorus, Rolf Vector Pro wheels, Selle TransAm saddle, Cinelli Integralter bars. Perhaps not a totally state of the art cycle, but as close as one can get without spending a king's ransom.
Trek weighs in at 16.8 pounds, Falcon is 20.9, or 20.3 if the Brooks saddle is replaced with a Fizik Pave. (why would you want to? The Brooks feels great) Trek has 30 speeds (10x3), Falcon has 12 (6x2). Trek has clip in Campy Chorus pedals, Falcon has the old chrome steel cage Record pedals, still smooth as butter.
In high speed downhills and sprints the Trek is noticably faster, and seems to achieve a higher speed, though no hard and fast measurements have been taken yet. On level ground, the Trek seems to average maybe 1 mph faster, in the informal 20 mile runs I've done, but that's only a couple of runs over my favorite circuit. My gut feel is that the Trek isn't substantially faster on level ground. This tends to bear out what I've heard about the radical aero wheelsets - they mostly help in high speed situations, but aren't that much better on level ground.
Curiously, the presence of only a 6 spd on the rear doesn't seem to limit the Falcon that much. The 10 spd on the Foil is nice, but not absolutely necessary.
The old Falcon has a more pleasant ride to it, though it is by no means flexy. It feels firm, but not overly stiff. (the Ernie Clements designed Falcon frame was one of the best of it's day) And I still love those old tapered Campy brake handles. On the other hand, you will never truly appreciate indexed shifters until you get on a bike with the old downtube shifters. Every shift involves reaching down, throwing yourself just a bit off balance, moving the lever until you feel the shift, and then getting back on the bars. Also, the Chorus brakes on my Trek are decidedly stronger than the old Record brakes.
Note to Campy fans: The Campy NR gear on the Falcon appears to be original equipment - rear derauiller is dated 1973 - and is still in perfect working order. No slop, no free play, nothing worn out, everything still looks great and works great. Pretty good for 30 year old components.
There is one other area I have to comment on - fit and finish. Here, it's no contest at all - the 30 year old Falcon stands head and shoulders above the modern bike. Chromed head tube lugs beautifully blended into the frame tubes. Same with the Campy fork ends - immaculately brazed, and then plated. Paint still has a mirror finish to it, excusing the scratches and smudges that 30 years have left on it. Contrast this to the Trek's average paint job (remember the Foil was their top of the line bike in 1999), and the Foil is by no means alone, the majority of high end new bikes I've seen have at best perfunctory finishing. None of them have the craftmanship that was put into this old Falcon.
If you're really curious, you should be able to pick up one of these classics - Raleigh Professional, Schwinn Paramount, etc... in the mid to high hundreds. Contrast that to what $500-750 will buy you in a new road bike, and that's actually a pretty good deal.
One final surprise - I loved those old steel cage Campy pedals so much, I thought I'd get on ebay and pick up two pairs for my tandem. What a shock - in good condition, the darn things bring over $100 a set! Apparently, I'm not the only one who remembers how terrific those old pedals are.