I think 10/15 percent is actually abitrary and not really that helpful.
25 years ago I was told about the 10/15 percent thing (by a dealer) and was uncritical (sadly), just accepted it. It was generally the advice given by magazines at the time, and I suppose it could be seen as a sensible 'ceiling' as it may possibly steer people away from spending idiotically disproportionate sums on cabling, but on the other hand in reailty, it does seem to have the opposite effect. Anyhow, I do think that there are a load of cables that could be good below £10 to £15. But then it's not my money, and there's more to cables than the sound in my experience - expensive good looking cables can give you a warm glow ;-)
Just for the record I've got:
Audioquest crystal hyperlitz speaker cable - £35 per metre (approx) if I recall correctly
Audioquest flx-slip 14/4 speaker cable - under < £6 per metre
Van Damme Pro Blue 2.5mm speaker cable - < £3.50 per metre
Van Damme Pro Blue 6mm speaker cable - < £7.00 per metre
I'm currently using Van Damme Pro Blue 6mm, which would be considered stupid and overkill by many here. Admittedly my current system didn't cost a great deal but that said, nowadays I couldn't bring myself to go over £10 to £15 per metre regardless of whether my system cost £1000 or £10000. That's my ceiling! Whilst I can hear differences in cables - and some differences are clearer than others - I couldn't justify spending larger sums for such a small benefit. I don't knock anyone for doing that by the way, just I cannot see the logic in spending £1000 on a cable to make your system sound a little bit better than it already did. On the other hand I wouldn't go the other way and buy a cheap, ugly (or even pretty) cable for £2 per metre because there was an idea that cables are all the same as so will be as good as anything else being sold for 20 to 30 times the price.
There are lots of reasons for wanting a particular cable - aside of improving sound, and quality connections etc. If you like cables that look the part as well and cost a bit more because of it, then so what, spend a bit extra and enjoy them for that. Doesn't really matter if someone thinks you are crazy because appearance is important. People don't like ugly hi-fi either, even if it sounds good, so buying good looking cables that don't mess with the sound amounts to the same thing. My Crystals were always commmented on when first seen...looks like very posh hosepipe
Anyhow, hope you find something you can live with. I've got some £7 per metre blue hose pipe at the moment (see above). It also 'matches' the cable used for my home cinema which pleases my wife..she really didn't like the look of the grey Audioquest ...told you there were different reasons