Wheels and Gearing for Mixed Road/Gravel--and SBT GRVL

Equipment
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Long time reader…

1.5 yr TR user… (FTP bump from 300 to 343. Thanks TR team!)

First time forum question asker.

Took the plunge and picked up a Cervelo Aspero w/ Ultegra RX and snagged a slot in SBT GRVL. Looking to pick up a second set of wheels for racing–which influences gearing choices.

Also will be racing local mixed road/gravel (80% road; 20% gravel) races ideally on the same setup (different tires–obviously).

Could use some input as I’m outside my expertise.

Found two wheelsets that appear to be good candidates.

Mercury is available on a Shimano freehub.
Reynolds on a SRAM XD Driver.

Questions…

  1. Does anyone have experience mixing a SRAM cassette w/ Shimano groupset? Noticeable degradation in shifting performance? Setup louder, less smooth, etc.? Recommendations on chains?
  2. Does anyone have experience exceeding the total capacity of a derailleur? Ultegra RX listed as 39T. Ideal to pair the 50/34 with a 11-34, 9-34, etc. SHIMANO ULTEGRA RX Rear Derailleur 11-speed | SHIMANO BIKE-EU
  3. Recommendations on cassettes with a wider range? E.g., XCX Plus 11 Speed Cassette
  4. Recommendations of other good values on wheelsets worth considering?

Any and all opinions/musings/hecklings welcome.

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I ran an 11-40 cassette with 50-34 cranks on a medium cage ultegra derailleur, + wolf tooth road link. Worked fine.

I think generally you can exceed the stated derailleur capacity by 2, maybe 4 links and be fine without adding something like the road link.

My gravel bike has a GRX drivetrain 48-31 cranks and 11-34 cassette. This is perfect for the gravel I ride.

There are a few road descents in the SBT GRVL where you’d be spun out with a 48-11 top end, but better to just coast at that point anyway.

I take it your cranks are 51-34? I need the 11-34 easy gear. Your FTP is higher than mine. You’ll be fine on 34-34 as your easy gear - for SBT GRVL anyway. The steepest climb is a short section on the road in the last quarter of the race with some 10-12% sections.