Both OS and Enya plugs have always been "medium" reach and why this is no one seems to know. However, based only on my 40/46 VF's, a medium reach is too short while a long reach is a fraction too long but not enough to worry about. Enya at least seem to machine their heads to suit a medium length plug although a long reach with an extra washer fits very well.
Of you don't want to take the heads off to check then I'd use a short or medium plug for the 10 and maybe the 15 while a long reach would be fine in the larger engines. For heat range I'd go with a hot plug but brand is up to you because everyone has their own ideas. Personally I use Taipan plugs.