I tend to judge it along the stack. So when the Ryzen 5 3600 was £150~£160,a Ryzen 7 3700X at say £300 wouldn't look so hot. But OTH if the Ryzen 5 is £270 and the Ryzen 7 was £320,I would rather stump up the extra cash and get the Ryzen 7.
But going by the fact you can get a Ryzen 7 5800X fairly easily for £330(and apparently others say around £300),the Ryzen 5 5600X should really be more around £240. In line with the Intel competition(£180 Core i5 12400F),if we say you need to add an extra £40 for an Intel motherboard,then probably around £220~£230 at least at current relative motherboard prices to be similar value(I think the number Humbug came up with).
Only thing is AMD really needs something under £200 - I think the rumours are its a Zen2 APU with no IGP?
But the days of £150 6 cores are well over. TSMC have increased prices by 60% since then and demand for AMD parts is mental currently.