I love the new V-Ray RT. I got a speed boost in nearly all “old” scenes rendered in Adv. And thats only with one GTX 980 ti. Here is an example:
OK, the grass (itoo Forest) looks different but I reckon I’ll figure out why. Any suggestions?
Regards
Check the shaders assigned to the grass. If you don’t find anything, feel free to send me a scene (grass and lighting only).
Yes, production rendering with RT does feel snappier than before. I like it. 
I remember that 3.5 cleared the progressive buckets/patches slower. I’ll probably make some comparison tests vs Vray 3.5 when I have some more free time to see if there’s indeed a speed boost and how much.
RT doesn’t support forest pack tint maps and also translucency maps on 2 sided shaders. I think one of those would be your problem. Also the edge mode in forest pack which is often used for getting nice clean grass edges doesn’t work in RT.
Yes, you’re right, the Forest Color mapped tint is the culprit.