Selftacker vs partially furled genoa - the selftacker would win every time.

Full genoa vs selftacker - the genoa will win as long as you are not overpowered. It also gives you the advantage of more sail area on downwind runs.

My feeling is that if overpowered, a full genoa combined with a reefed main will give better performance than a full main + selftacker.

Something I take into account during racing is the level of crew experience/competence. If you expect to lose a lot of time during tacking due to unpracticed crew, go for the selftacker if you have the luxury of choice.

I would also agree with the above. I have myself both 1) full genoa and 2) self-tacking JIB. 99% I am using the self tacking JIB, but the genoa only when sailing long passages with sidewind. Even in high winds I have never used the jib furled as it loses the shape quite easily (and same happens to the genoa).

But purely performance wise, in low winds naturally the genoa is better, but if there is any need to reef/reduce sail area the self-tacking jib will always outperform a furled genoa

For me it was the other way around, I only had a selftacker and added a genoa causing a 1 point penalty.

Just want to chime in here. I did race with a self tacker, it had some advantages, namely better rating against Impala, MG27s and similar, so in 15kts plus we did rather well, and self tacking meant we could short tack much more confidently down some of the narrower channels in Poole Harbour. Much less drama and shouting and the crew just needed to slide across the deck.

One thing I did do was to use two ordinary sheets as well as the self tacker so that off the wind there was a much better sail shape, the self tacker can really mess up the shape offwind. The downside is more string in the cockpit though.

It also allowed me to three sail reach - see picture, we were doing nearly 9kts - which usually worked well, until we were overpowered. However, with lighter winds we were at a disadvantage, so in the end I had an overlapping genoa made which changed the rating for the worse, but overall we did just as well, and weren't frsutrated when the wind died down. We still sometimes used the self tacker when the winds were 20kts+ to make our life easier.

Now I've stopped racing, I've gone back to the self tacker which is a lot less work when I'm on my own. 

Is that an symmetric or asymmetric spinnaker?

Thats a standard symmetric spinnaker. When it was measured for rating it was: