New Carbon Wheel options for a Mason Definition

Go hand-built- speak to David at DCR Wheels - you won't buy anything else ever again!

I really wouldn't bother with the Hunt 35's.  You save 109g & £100 over the Aerodynamiscist 44's but lose out massively in aero on the flats and downhills.  You'll only be doing L'Etape once and 100g is about 1/6 of a water bottle.

I have a set of the mixed 44/54's and I would recommend them.

The 44/54's have one of the loudest freehubs I own louder than my 2 other Hunts (even if alledgely the same sprint hubs).   Almost as loud as my Hope MTB's.

You can mute it with a blob of grease apparently.

I would add the Vel RSL2 to the running - primarily because they come with DT Swiss 240 hubs rather than the "own brand" hubs supplied with the other wheels.

Maybe I'm unduly skeptical of the own brand hubs (I believe they are produced by well established hub manufacturers such as NovaTec and Bitex before being re-badged) but personally I have greater confidence in both the reliability and the repairability of branded hubs. 

I've got the hunt aero wide 50's too and they're great for the money but the freewheel is insanely loud. I've had them on my canyon endurace for 2 years now and had zero issues. 

If you want lightweight, stiff, excellent value and bombproof build then I suggest looking at Scribe wheels. 
I have Hunt limitless 48, limitless 60 and Scribe Aero Wide+ 50. I prefer the looks and performance of the Hunt wheels over the Scribes but the Scribes more than punch above their weight for the price.