Which one of the three: Shimano DA 7800, SRAM Red with Ceramic BB, FSA K-Force Light? Am I missing any others I should be considering besides DA 7900?
It’s a crank. Flip a coin or pick the one you think is prettiest. They all work the same.
Non of the above. I think the best bang for the buck right now is a pair of Zipp 300’s on Ebay for around $250 give or take a bit.
Using the new K-force light (110 bcd: run 52/38 or 50/36 or 34 depending on use/course). Had issues with previous FSA cranks, but this one has been great (over 5K miles). Like the weight and the ceramic bottom bracket and annodized red cups it comes with 
Only reason to “upgrade” a crank is for weight reduction or looks though.
Using the new K-force light (110 bcd: run 52/38 or 50/36 or 34 depending on use/course). Had issues with previous FSA cranks, but this one has been great (over 5K miles). Like the weight and the ceramic bottom bracket and annodized red cups it comes with
Only reason to “upgrade” a crank is for weight reduction or looks though.
What are people’s opinion about upgrading and changing size? I bought a bike (new) on ebay. The spec for the bike (a 51 cm P3C) was for a 170mm crank, but when it arrived I discovered the crank was a 172.5. I have thought about upgrading to a FSA K-force light in 170mm as my bike fitter recommended 170mm cranks, but I have not been able to convince myself to spend the money for a marginal change in weight and resistance. I am not sure if I would even be able to feel the 2.5 mm difference, and we are talking over $400 here even on ebay. Opinions?
Only you can decide if it is “worth” $400. I can tell you that you will not be able to “feel” much, but you will loose some weight, and should likely be on 170mm cranks with a bike that small (better for toe overlap and spinning on a tri bike).
If money is an issue (to some it is, others not), $400 could certainly be better spent elsewhere (aero helmet, training camp, wheels, etc.)
You could always post here on ST for someone who has a set of 170 that wants to trade for 172.5’s. That way you won’t be out the cash and you can use the money for other goodies.
Here is a link to reviews of many cranks … lots of numbers and pictures…
I’d be inclined to go with DA 7800. It’s pretty much the standard in stiffness, it’s a decent weight crank at 775 grams, and can be had right now for around $300.
Otherwise I’d agree with BMAN. Online retailers can’t give the things away even at $300-350 even though the crank with rings weighs ~460 grams.
Just curious…
Anyone know the lightest option for having 165mm crank arms? I think I’m stuck with Shimano Dura-Ace and SRAM Red…
i kind of went through this recently to upgrade the stock fsa gossamer on my felt b12…
i went the the dura ace. shifts much better than the fsa. i had also considered the zipp 300 but after additional cost of an isis bb and questionable reliability on other forums, i stuck with durace. you can get new dura ace cranksets on ebay for <$300 and bottom brackets are only $20-40 depending on the finish you want. add another $100 if you want ceramic bearings (not yet for me).
also, i went from 175 to 170mm and what a difference. much easier for me to spin now in the aero position. i still ride 175 on my road bike.
have fun,
jksu