Hi,
I can't comment on anything apart from the X5 and X10, however my personal viewpoint is that the X10 is a huge step forward over the X5 in terms of sonics. Of course this is personal opinion and I have read posts from others who say there is a very small difference between them and some who think the X5 is the better earphone. I previously wrote here that I would not be surprised if the X5 and X10 were designed on different planets, such is the huge difference between them.
I found the X5 to be clear and reasonably smooth, but very emasculated in the bass and top end. Especially as a result of the top end, it did not do any favours to recreating with any credibility the timbres of instruments known to have strong harmonics at high frequencies (i.e violins). They also seemed to be compressed dynamically and just lacking in any sort of toe-tapping listening involvement. It was lacking in both detail retrieval and soundstanging, making listening a rather boring experience. It was the auditory equivalant of watching paint dry. Mind you, most IEMs I have ever heard sound pretty awful, including the Shure SE310 and Westone UM2.
The X10 to me is a totally different product. Extremely well balanced, smooth, extremely clear with very good detail retrieval, a top end as good as any in ear design I have ever heard and excellent imaging.
Where the X5 wins out in my experience is comfort. I do actually find the X10 pretty uncomfortable for anything other than short listening sessions (i.e less than 40 minutes), whereas I could have worn the X5's all day. The problem is that the black tails on the X10 curve round in a shorter distance than they do on the X5 and as a result of this they make contact with my outer ear. There is no way to avoid this contact unfortunately and it results in discomfort after around 45 minutes. The tail on the X5 however, is larger and does not make contact with my outer ear because the "bend" radius is larger.
I am not happy with the durability of the X10 - already after only two months the rubber on the tail has slightly deteriorated, even when taking extremely good care of them. Again the X5 has an advantage here because the black tail is larger and thicker and therefore I would imagine more robust.
All said and done, I doubt anything I have written here will be of much help to you, since for every comment I have made, there will be many people whose experience is completely contradictory.
Perhaps one thing to consider is to buy from somewhere overseas such as soundonearphones. If you are not happy with the X5 you can then return them for the X10, or vice versa. I realise with the very weak dollar buying from the US is not attractive these days, but if you by in Australia you will be stuck with whatever you buy (and Klipsch prices have just gone up quite a lot in the last month too). You then have to weigh up what you will get for them if you put them up for sale versus the extra cost of having bought from a place that allows exchanges.
BTW, neither the X5 nor X10 remind me in any way shape or form of the full size Sennheiser house sound. Whilst I would say the X5 is furthest away from the Sennheiser sound, that is like saying Russia is further away from Australia than Japan is. The exception is that I consider the X5 reminds me a lot of the full size PXC450 with the noise cancelling turned on. I suppose I would call the X10 a bit darker and warmer than the X5, though only because I find the sound of the X5 to be rather sterile (in other words the X10 to me sounds completely normal).
