Thanks Simon!
The Ace Interior oil varnish (recommended by Bruce BTW) seems harder than Rockhard, itself harder than Tru-oil.
That being said, oil varnishes tend to harden and become tougher with age, and kind of self-polish if I may say. It's very organic.
I do not know if it's OK to post varnish-related links since I am not a sponsor here (John, delete the post if it's not…), but here is one finished with Ace interior oil varnish:
B-2
And one finished with Belhen's Rockhard:
A-2c
Notice the difference in colour, pics taken outside the same day (same light).