As someone who has been using Rock Throw/Stone Edge for about 6 months, Rock Throw/Rock Blast is very comparable.
And that Mud Slap/Rock Blast combo is going to be solid defensively after gym rework, regardless of its type disadvantages.
Mud Slap/Stone Edge is still very, very solid, and I'd hold onto it to see how moveset changes might alter DPS.
Same with Mud Slap/Earthquake.
All in all, if you must invest now, I'd suggest the Rock Throw/Rock Blast, though personally, I'd recommend waiting until the next moveset update to see how things shake out first. I've invested far, far too much dust into mons I thought would be tanks forever, only to see them nerfed into oblivion weeks later (here's looking at you, Ice Shard/Ice Beam Lapras and Bubble/Ice Punch and Bubble/Submission Poliwraths...).