Hi Richard,
I don't think the 1858 with smaller numerals (not 8/6) is particularly rare.
London Coins past auctions may not be the best place to assess this; a quick look at ebay reveals at least 2 on there at this moment.
I have sold quite a few 1858 smaller numerals over the years, and have examples from 5 slightly different smaller numeral obverse dies in my own collection.......including the large rose type with the flaw through the 5.
These can be seen below, noting some slightly different numeral locations in respect to border teeth, and the different repairs to the second 8. The large rose / small date being at the bottom of this set of images.
I'm sure that there will be more examples than your 20 limit for 'rarestpennies'.
Hope this helps,
Ian