How can you seriously compare someone who plays virtually nothing but modern repertoire? Firstly, it's anyone's guess how accurately such music is performed. You can't judge it unless you know it intimately. Even then, they can get away with a hell of a lot more than somebody who plays a large repertoire of tonal music. Secondly, there are absolutely loads of specialists who play reams of modern repertoire. I'm not saying he necessarily isn't uniquely talented, but I don't know of any real evidence that would make him stand out from all the others- including Jonathan Powell.
A good point but one that needs a little expansion, I think. Mr Pace does indeed play works other than those that could be categorised as "modern" repertoire and, indeed, I have heard him do so; I accept, however, that it is for the performance of quite a wide variety of contemporary repertoire that he is best known. I do not entirely accept your contention that you "can't judge it unless you know it intimately" because, if you can read music and follow Mr Pace's (or indeed anyone else's) performance with a score (not that you'd necessarily have to do this), you could at least get some idea of the textual accuracy of his (or anyone else's) performances. People who play some of the more challenging of contemporary repertoire (and not just pianists, of course) might indeed "get away with" all manner of things provided that they're not performing in front of people who can read scores; the English soprano Jane Manning, who has been respected internationally for her performances of contemporary vocal repertoire for some half century, would agree with you - she told me many years ago that some of the less talented singers who try to make a career for themselves out of specialising in contemporary music performance would be shown up for what they are if they have to sing Mozart and Handel (she added that if you can't sing those two composers you can't be guaranteed to be able to sing well anything that's worth singing).
Personally, I am very impressed with Mr Pace's facility in terms of general digital dexterity, hand/eye/brain co-ordination and signth-performing ability but sadly far less so with him as a performer in other departments; for example, I once heard him play
Turandots Frauengemach from the Busoni
Elegien and I found it quite alarmingly empty and unengaging. Jonathan Powell, on the other hand, seems to have performed a good deal more non-contemporary repertoire in public and, having heard him in Chopin (albeit only some of the composer's late works), Alkan, Rakhmaninov, Skryabin, Granados, Albeniz and others, there is ample evidence that he can hold his won in this repertoire and his attitude towards the most obviously demanding music that he's performed - some of Sorabji's works (indeed far more of them than any pianist in history) - that it's simply a matter of quantity rathe than difficulty per se - has held him in very good stead when presenting it.
Sorabji's
Concerto per suonare de me solo, whilst by no means one of the composer's larger works, is an absolute killer in terms of physical and mental stamina, co-ordination and demands on the reflexes, yet Jonathan Powell plays it as though it's the kind of repertoire that pianists play because it's there and it's important like Chopin, Liszt, Alkan et al.
Best,
Alistair