I'm roughly the same weight, from an MTB background and love hitting the descents and corners hard, so as a cross-the-globe-BFAM, I thought I'd offer the following comments... nope apparently it's an essay - sorry about the length!
I rode Ksyrium SL's in 2005. They felt stiff, delivered power well and I thought they looked good at the time. I then moved to DA C24 wheels and noticed an improvement in ride quality, with no disadvantages (even the weight was technically better, as the wheelset weight was fairly equal, but it was located more at the hubs). After that, I spent a few seasons with Reynolds sponsorship, which I'll skip commenting on.
For the last few seasons I've worked for a travel company and built up my own wheels to ensure that I have the maximum possible ride quality for long days in the saddle, while still having wheels that keep my bike light going up and strong to rip out any stresses on the way down. Because our bikes get sold each season (with wheels obviously), I've had a chance to refine things a bit year on year. As it sounds like you're looking for the same qualities I prize in my wheels, I thought I'd share my formula:
- Novatec Hubs (A291SB & F482SB are my pics), which I first rode during my Reynolds days and found to be a very good balance of weight, performance and especially price - plus their sales service has been excellent. Theses hubs held up better then my Ksyriums did in dry weather (my mavic rear hub got a banshee stuck inside after one season). If you ride often in poor weather and aren't keen to do any servicing/replacement of bearings (I did need to replace one of mine after a UK winter - but that's true of almost every hub I've had), then you might want to look for something more robust - even if you'd just prefer to have something a bit more bling. But the Novatecs definitely get my vote for quality, high-value hubs, and they allow me to spend money on rims, which have a much bigger impact on the performance of a wheelset.
- spoke count is 20h front & 28h rear. I'd done 24h rear for a racing set in the past, which required a bit more work to keep true. For the weigh of four more spokes, 28h rear keeps maintenance to a minimum, which is what you want for a set of every day wheels. As Zen mentioned, 28h seems right for guys our size - especially if you want a wheel that sprints and punches up hill without hesitation or the dreaded brake rub.
- DT Aerolite or Sapim CX-Ray spokes on the front - the best thing is they come in boxes of 20, so it's an easy purchase, but I've found these to be the best option for ride quality on the front wheel, while also offering some aero benefit where it can have the biggest impact.
- For rear wheel spokes, bladed isn't really necessary (you could easily just go with DT Comps), but I've preferred it for consistent looks. I've run aerolite/CX-Ray on the NDS, and then my best discovery has been running heavier bladed spokes from Trek (Bontrager) on the DS, which are MUCH less expensive then aerolites, offerd in loads of lengths and because the Novatec hubs are slotted for aero spokes, these build very nicely into a strong wheel.
- Rims have been a more progressive adventure. At first I used HED Ardennes, which offered fantastic ride quality and performance, but were expensive and wore pretty quickly on the brake track. Second set was built with C-4 V22, and I would never deal with that company again (they even flat out lied about whether they had sent things yet) - the rim was okay, but not a full oversize rim and the pinned join was noticeable when braking. I've now built with Archetypes, which have built with excellent quality, have a proper machined brake track and solid 17mm ID to allow the tire to sit at full width - which means you have the potential to boost both comfort and cornering/braking performance versus the tire profile of the Ksyriums.
Perhaps most importantly, these wheelbuilds have cost between £250 & £400 for the sets, so it seems that even paying for a good local builder, they are all well within your budget of getting below the Ksyriums.
One additional comment if I may - if you're 80kg and feel that your front wheel gets thrown around on windy descents, I can only suspect that you aren't particularly well balanced on your bike - that you must not have enough weight on the front wheel. Are you in the drops while descending? If not, get down there, keep your weight LOW. If it feels like you have too much weight on the front wheel, then move your weight back a bit, but never up. Also try to progressively get more comfortable with increased weight on the front end, because at 80kg, you shouldn't be getting blown around on Ksyriums.