So I got the Rotor 55-42 chainrings. As mentioned, had to remove the power meter from the crankset, but that was fairly straightforward (I never used sealant glue so it came apart easily when I put it in a vice). Got the new rings on easy enough but problem with the chainring bolts brushing off the chainstay - or maybe it was actually the brake calliper (it's an integrated brake behind the bottom bracket). So I took it off and turned the chainring bolts around so that the side with the less protruding ends is facing inwards and this is just about clearing the chainstay/brake calliper.
If it does prove problematic and starts brushing off the chainstay/calliper under strain, should a 55-39 combination work (I know the 39 has no issues with brushing off other parts), or is that gap between the 55 and 39 chainrings too much of a gap when shifting and/or for chain length? I put on a new chain and sized it by running the chain directly over big sprocket (11-28 cassette) to big chainring (bypassing the rear derailleur) and then adding 2 links, and it seems fine.
Changed the aerobar TT shifters at the same time as I had damaged the inside of one of the shifters after reassembling it incorrectly after changing gear cables (the little black bit that falls out and seems to control indexing got blunted) and I'm having a problem with rear shifting - when in the small sprocket at the rear, when I shift up, the first click (and sometimes second click) does nothing. After that, it shifts reasonably ok, but the initial shift is a problem. It's these Dura Ace 7900 bar end shifters: https://www.chainreactioncycles.com/acc ... 1921867879
and it's Ultegra front and rear derailleurs (couldn't find 10-speed Ultegra bar end shifters online).
To double-check I hadn't set the derailleur up wrong, I went back and redid the adjustments, following this video https://www.youtube.com/watch?v=wQncKmddahk
. All seemed ok, though I did notice the b-tension screw doesn't seem to have the usual effect as I don't notice the jockey wheels moving up or down as usual. Wonder if there could be an indexing compatibility problem or perhaps something I did incorrectly in the derailleur setup (which was basically to set High limit screw, undo and redo cable to reset tension, adjust tension with barrel adjuster, then do Lower limit screw)?