Wheelset upgrade from R501's

If you can try some different wheels (especially trying the difference between deep rims and non-), I would recommend it.  How you feel with the wheels will probably have a greater impact than most other factors (across a relatively narrow price / specification range).  Also, clearly there are a number of people who find deep rims a handful in crosswinds, but personally, I've never found it an issue - I can only really recall one instance where I noticed it and that was when I was hit suddenly from the side by a very strong gust.  You'll also get a sense for the difference in stiffness when putting the power down.

I have had some extraordinarily light Planet X deep rim tubulars for a few years, which I love (and were very reasonably priced).  They don't still make the ones I got, but I don't think they'd be what you need - when I'm putting the power down (especially out of the saddle on short uphill segments), the lateral flex is very clear. By buying low price, but very light deep carbon wheels, I sacrificed lateral stiffness (although this is not an issue in the slightest for the overwhelming majority of my riding).

Finally, if buying carbon, do check the maximum recommended weight of the wheels you are buying.  As an example, ISTR that mine are recommended up to 90kg.

I'm a heavy guy too and after much research for one pair of wheels for all round fast road use I went for citec cx6000s last year.

They are very strong and lighter than most, with alu brake track (no carbon brakes thanks!) and some aero benefit. So far i am very pleased with them.

If you hunt around you can usually find them on sale somewhere in germany for about 600 quid, which might be a bit steep, but otherwise could be worth a look....

As a heavier rider, you'll probably benefit more than others from the deeper section rims in windy conditions as you're less likely to get blown about. But I'd advise getting used to them in a variety of conditions before using in a group. The stiffness of carbon/ aero rims will help you too.

Keep in mind that deep section rims catch the wind, which you might not want if you are also using them for road events / riding.? I find the R501s plenty stiff enough for me, but I know my brotehr in law who is more powerful rider who tends to mash his gears can get brake rub on them. To get a stiffer wheel you will need a deeper rim, more spokes or higher spoke tension.

Have you identified the TT bike you want to buy? If that comes with decent deep section wheels then I don't think there would be much point buying another deep set of wheels now as you would just end up with two lots of wheels that are basically the same.

Are you wanting to justify new wheels or are they genuinely not up to scratch? Have you serviced them? My RS80s are lighter and a bit nicer but it's not a night-and-day difference.

I wouldn't bother with deeper rims unless you're racing, you're just paying for extra carbon. As I and others said on a similar wheel query the other day, I'd opt for handbuilt if buying now.

What do you mean by a tad wobbly? I race cyclocross on R501s and they aren't light but they are certainly very robust.

I upgraded from R501's to RS81C24's and the difference in ride was really noticable. The RS81's spin up quicker and the dampening effect over rough roads is huge. They have really come down is price since I purchase them too! Highly recommended! 

I'm running Fulcrum Quattro CX as my winter wheels - picked them up about a month ago. Spin up relatively quickly and hold speed, bullet proof and take the Conti 4-seasons 25c I'm running on them well. Not the lightest of course and it really depends on the conditions you plan to use them on and if you are climbing, or mainly on the flat.

You'll save 100g with the Ultegra wheels and they are equally bombproof... if not a little narrower.

Either would be fine for training or sportives, anything more than that and I'd be saving for something a little more expensive - or taking advantage of some good sale prices at the moment.

HTH