My road bikes are both older, 7-speeds. The steel Ironman (172.5 crank arms) now wears 50/39 chainrings and 13-25 freewheel. The early '90s Trek 5900 (170 cranks) is 52/42 (Biopace -- hey, they're okay with me) and 14-28. On fast downhills I'm often spun out at 130 rpm, where I get a bit wobbly and can hold that cadence for only 15-30 seconds. And on bad days neither has a comfortable granny gear when my legs are dead.

My favorite gearing? My old 8-speed Univega hybrid (175 crank arms) with 50/40/30 triple and 11-32 cassette. I've never spun out on fast downhills (partly because of wind resistance approaching 30 mph with the more upright bike) and always have enough gear for climbs even when my legs are dead. The bike never really feels like its 30 lb weight. In contrast, some days the 20 lb Trek feels like a lead sled, usually the final climbs after a hard (for me) 30 mile workout ride.

Eventually I'll convert the Trek 5900 back to 8-speed, 11-32, and might consider a 52/38 double in 130 BCD, unless I switch to 110. We don't have any long steep climbs so that would be adequate.

Yeah, the crank arm lengths might make some difference. Honestly, I'd need better data over time to be sure it's not just subjective.