Browsing the internet has revealed a vast array of possible bikes, and yes, I do need to narrow down my options...
I tried a couple of bike shops over the weekend, and wasn't very successful. In the first shop, I was met by a spotty youth who opened a Specialized catalogue at the women's specific pages... I could tell something wasn't right with them, and didn't recognise the names... Unsurprisingly for this time of year, they had almost no stock.
The scond shop looked more promising, with the guy seeming to know what he was talking about, but we seemed to get off on the wrong foot when I suggested that I'd like to try a small frame, since I have a short upper body and long legs; on previous bikes I've been over-stretched, which ends up with sore shoulders and wrists. I think he took the hump that I didn't trust his professional judgment by looking me up and down for sizing.
Oh well, that's two shops that won't be getting £2k5-£3k's business (not that either seemed particularly bothered; anyone would think there isn't a recession...)
My thinking for the XC bikes was for their light weight (being a lightweight myself), rather than racing, but I'm beginning to think that a more relaxed bike like the Stumpy FSR might be more suited to what I'm actually likely to do, especially considering that XC bikes seem to be a little longer on top tube to encourage a more forward-balanced stance. I confess that I'm still getting to grips with the nuances of the various terms...
As for fitting new bits to my old Rockhopper; that's a no-go; it's too big for 'proper use' at 19" (first bike bought in a hurry after my road bike got written off when a woman pulled out of her drive in front of me...). That got nicked a couple of years later, and then I found it in town a couple of years after that, and recovered it in a somewhat sad state (with sizeable dents in the top tube). It's okay as a gash bike for cycling to work and back, but I haven't trusted the frame off-road since I recovered it. The 17" RH I found to replace it also got nicked a couple of years later... Did someone say Specialized bikes have good resale value? The thieving scrudgers obviously think so...
I had to put a shorter stem on the 17", which is what made me want to try a smaller frame.
Thanks for all the suggestions; just have to find shops that have bikes in stock and see if I can get test rides.