I GM a steam-lined RMX. Here are the tweaks I've made:
-I use a single armor skill based on RL development cost.
-I develop Weapons based on group (1 Handed Edge, Missile, etc).
-I replace climb & swim with Acrobatics (Ag/Qu) & Athletics (St/Co) - this gives a generic Ag & St based skill roll.
-Ride is a generic animal skill.
-I use a single Lore skill (no sub skills) and a rule that all rolls relating to your profession, race, culture start at Light difficulty and each step beyond that increases the Difficulty by 1 step (this leaves a little world based interpretation).
-The other 3 secondary skills are staples in my games anyway (so they are essentially primary skills).
-I use Concussion's Ways as 1d10 healing/level - each d10 can heal a d10 hits or 1 pt bleeding, or 1 round stun or -5 in penalty.
I have changed the dice rolling to a TN system of Light 70+, Medium 90+, Hard 110+, V.Hard 130+. These numbers are based off experience and making them achievable for players from levels 1-3; not be totally derived from RM rules.
You can also reduce the attack tables to the core 4: 1HE, Missile, 2H and Tooth & Claw....honorable mention to the Ball table..but, that doesn't get used all that much.