Ultegra wheels upgrade on Tarmac comp

I think you are tad too sensitive.  
The collars and cuffs metaphor was quite good.
Since you are commuting and also thinking of competing, you are going to want two sets of wheels, anyway, aren't you? The ones you've got are probably good enough for everyday use. You don't have to hurry to spend another thousand quid or so on wheels. 
It takes a while to understand all the ins and outs, the compromises between strength and weight, of the various bits of bikes. Download a spokemaker's catalogue and you will see how arcane even such a basic component is.

Without experience, it's probably best to start by finding out the specified weight of your wheels and work out, by looking at other wheel specs, how much weight you can realistically save. You could also find a wheelbuilder near you and chat about the options. At the higher end, independent wheelbuilders are cost competitive and do as good a job as the big name manufacturers.

What - apart from matching collars and cuffs - do you hope to achieve by 'upgrading' to an Ultegra wheelset? 

As I understand it the Fulcrum S4 wheels are made up of bits of S5 & S3.  They are similar in weight to Ultegra and well regarded, it seems.  From what I can gather the only possible advantage of the 6800 wheelset - if you are so inclined - is that they are tubless ready and all that, whereas the S4 are not.  My humble opinion - stick with what you have until the rims are worn down then get the 6800 (or 6900 by that time?).