I've got a 20 km loop that I like to ride from time to time - actually, it's 21.3kms but I think of it as my 20km Loop. If you want to go more than 10k and leave from my front door, it's the easiest loop in this area ... which is rather sad when you look at the profile below (courtesy of Bikely)
Yes, it does have all those ups and downs in real life (though being bikely, not necessarily all the jagged bits).
I rode it yesterday on the Europa, fixed gear at 70 gear inches (42x16) ... and it would be fair to say that I was a wee bit knackered when I got home.
My poor little HRM had hysterics for much of the ride and needed a couple of valium afterwards My average HR for the ride was 151 and it hit a peak of 179 (my max is 185).
Cadence - bearing in mind that on a fixed gear bike, you're forced to pedal all the way - my max speed was 52km/hr, which isn't huge but with that gearing, my cadence at that speed was 154 No wonder I was muttering 'chase that pedal, chase that pedal, chase that pedal'. That was on the hill just before the 6km mark. After that, I limited my speed to 40km/hr.
Average speed for the ride was 22.7km/hr which isn't huge but with all that climbing and not being able to open up down hill, not too bad.
Funny how tired my legs felt afterwards though
I decided to do the loop again today. This time though, rather than kill myself on the Europa, I took the Jamis (geared) and forced myself to keep my HR below 140. That didn't happen of course, there are just too many bits that go 'up', but I average 139 with a max of 168 so I didn't do too bad. Top speed was 51.4km/hr at a cadence of zero because I was coasting
The interesting thing is, my time for the loop was within a minute of yesterday's time and the average speed the same.
So, based on that evidence alone, I guess you could claim that gears do make a difference after all
Which won't stop me attacking the loop on the Europa tomorrow