Mavic Kysrium Elite or Hunt Aero Wide/Road

My stock wheels on my Synapse were terrible. Some Cosines with Novatec hubs were a night and day improvement.

On another note, are stock wheels really that bad? Since having my winter bike nicked, i've been riding a Genesis Croix de fer on some alex rims and basic shimano hubs and 32 hole spokes. I was intially looking to get these replaced ASAP but found I could still gun it around on these and hold the speed on the flats.  

My only gripe with straight pull spokes (especially mavics) is that they always seem to rotate slightly which really f**ks with my OCD.  If your going to chuck £400 at a pair of wheels, id weigh up handbuilts like H plus spon Archetypes with j bend spokes.  I used to have a lovely pair of these, but unfortunately they got nicked which is another story. 

Not ridden Kysriums, but have had a set of HUNT aero-wides, for about a year.  They feel like you're flying uphill over stock wheels!  The wear hole on the brake track seems like its shallower than my stock wheels were, I'm presuming this means not as much 'wear life' as a set of stock wheels but thats probably where some of the weight gains come from.  Of course that could just be my imagination, and I don't have any other 'lightweight' wheelsets to compare it to.

Keep the stock ones for winter use, and wear down the brake track on those with the winter paste!

As for customer services issues.  You will have ZERO and I think I can say that confidently.  I did have a minor issue with one wheel when new and they bent over backwards to sort it.  At zero expense to myself.  To be honest you'll probably get better and more personal service from them than you will from a big corporate like Mavic.

I've got Ksyrium Pro and and 2 sets of Hunt currently. The Ksyriums are as above - extremely well built, run smoothly and look like they will last many years. I have the Hunt Mason X and also the Carbon 30. The Hunts are great value for money and as above their customer service is brilliant. I've contacted them a couple of times and they are a pleasure to deal with. Out of all the wheels the Carbon 30s are my best set. They are very quick, ultra light and not twitchy in a side wind. I wouldn't be worried about any after sales issues with the Hunts as thy will stand by an issue even if out of warranty . 

I've got three sets of Hunt wheels now (or rather, I've got two and my girlfriend inherited a pair when I went from rim to disc brakes).

I haven't ridden the Kysrium Elites, so can't help there, but I'm really happy with the Hunts. What's really made the difference is the customer service, though, which is why I've ended up going back to them.  

They've been great every time I've dealt with them. I needed to replace the bearings on one set, and when I checked which ones I needed to buy they just stuck a new set in the post to me. And when I had a minor crash that wrote off a back wheel, they gave a pretty generous discount on a replacement wheel and had it in the post to me within a couple of days.

Thought I'd chip in, as you said that one thing that was putting you off was the small independent retailer angle. 

If it is any help, DT Swiss RR21 can be found for 470 on Rosebikes.de, whilst I remember their price was around 600 about a year ago.

I bought a pair of ProLite Bracciano 42mm wheels, rode them once and sent them back, the join on the rim was so bad on the back wheel that they were unusable.  Maybe one bad pair but that is my experience of them.  Have a look at Superstar's selection, some real shocking colour schemes if that is your thing.  https://www.superstarcomponents.com/en/shop/road/road-wheels/

https://www.slowbuild.eu/

I've had some Ksyriums for years and they've been faultless. Recommend.

If you're not a brand snob, these are very light for the money -

http://www.wiggle.co.uk/pro-lite-bortola-a21-alloy-clincher-wheelset/

I think they are comparable, but I would say go for Ksyriums. Few grams up or down won't matter, for the sake of durability. I think Ksyriums probably have more durable hubs than Hunt's Novatec.

Let me propose some other options for you:

-Handbuilt Hope Mono RS/RS4 or DT 350s with Kinlin rims/Mavic Open Pro UST/Sapim spokes.

-DT Swiss RR21 Dicut (240s hubs) - shop around, might be slightly more than budget.

-Campagnolo Zondas C17.

-FFWD F2A (240s hubs) - shop around, might be above budget a bit.

I own 2 set of wheels from Hunt. I have no complaints about their wheels or service, bearings are easily replaced, you get spare spokes with the purchase.

KEs are an epic wheelset.  My oldest set are the very first ones, and I've still to true them, because they are still within 1mm of true.  People take a whole load of badgers fetch about them being "harsh" and "unforgiving" etc, but it's complete balls - drop 5psi and stop moaning.  They really are a superb wheelset for tacking potholes, crappy roads and all the rest of it without issues, and over the ditch on hot flat roads they just roll on and on and on.  Ok, they're not (now) exotic, but they are superb.  Where's my endoresement payment?  Oh - probalby don't deserve one given how long they last.

I haven't ridden either but what I will say is that my Mavic Aksium wheels have outlasted 2 pair of Cosine (Wiggle own brand) and 2 pairs of Campag (Zonda and Vento) wheels.  Guess which make I am going to buy when I need a new pair of wheels!

Hunt have a sale on at the moment, a friend of mine bought a pair this morning.