Disc brake wheel upgrade – what’s best for 300-500 quid?!

I ride a 2015 Cannondale Synapse, the disc brake version, which I love to bits.  It was my first road bike 2 years ago and I’ve steadily got more into the sport.  This year I’ll be doing a few big challenges – a 350 mile ride from London to Germany (over 4 days), a sprint triathlon (to complete, not compete), and a few 60-90 mile sportives.  

As well as a general fitness drive (I was a bit porky, and have dropped 20kg!), I’m keen to upgrade a few bits on the bike, especially wheels.  I have about 500 quid to spend I reckon, including a new cassette, and better tyres, leaving maybe 350 for the actual wheels.  I’m interested in speed and aerodynamics, but also interested in durability and stiffness (I’m 6’5 and 90kg…). 

Finding disc brake wheels in this price range is quite tricky, they tend to be either much cheaper, or much more expensive. But I have a short list of a few: 
– Mavic ksyrium disc, which is about £290 for the 2016 version, or £330 for the 2017 version, and seems to be the best all rounder. 
– My local bike shop has recommended Hope 20FIVE Pro4’s, which are about £250, but seem a little heavy.  
– Forza CIrrus Clincher disc, £225, partly cos they look quite nice!
– Fulcrum racing 5 disc’s, £300 – local bike shop doesn’t like these…
– Pro Lite A21 disc, bit more expensive at about £450. 

There are a few other options of course, and likely a few that I’ve not yet found too.  

Is there anyone out there in the same dilemma as me, or any knowledgeable folk who know everything about wheels…?!