What's the difference between simple shimano R540 SL pedals and fancy ultegra 6800 pedals? The latter use more bearings? has better cage assembly? are the advantages real, or is it mostly hype? I've only had entry level pedals, but I'm curious what spending 2x the money will get me as far as pedals go.

The Ultegra (105 and R550 too actually) have a removable metal plate. Once the one on the R540 is gone, it's gone.

The Ultegra is lighter.

The rest of the information I have is stuff I read rather than facts : Ultegra being stiffer, wider and more reliable due to the carbon body and stainless steel axle.

I've used the R550 for a year then moved to Speedplay as I needed more float.

I have 105's now and had 540's before. Definitely lighter in the 105's as they are carbon.

Looks like the main difference is the CF body on the more expensive pedals and
about 3 oz weight per pair, which is negligible. Bearings and axle essentially
the same, disregarding unknowable metallurgic variances. Looks like the 540
has a replaceable wear plate as well if you look at the Shimano literature.
So difference is ~$15/ounce. Or you could pee before the ride and get rid of
twice as much weight....

I dunno. The weight weenies would disagree that the weight difference is negligible. That 3 oz is 85 grams and for $45 it's "only" $.52/gram. They think that's cheap!

Others may disagree but it's more important to reduce rotating weight than static weight i.e. saddle, so saving a few oz's on a pedal means a lot to some.

don't give a flying f-k about 85 grams. i ride a 19 lbs caad9. by the time 16 lbs bikes start to make a difference in my results, the bike will be sponsored, so that's that.

what's with the replaceable metal plate? is that the thingy in the middle of the pedal that makes contact with the cleat? I didn't even know that was a perishable item. I thought the cage would be the one to go first, and several sets of cleats before that? how fast does the metal plate wear?