Hi,
Each card has multiple PFEs (0-3) so it depends on which PFE traffic is received for MX240 onwards series.
There could be two scenarios:
(1) say if traffic is received on PFE0 of the FPC 1 (ge-1/0/1) and egress is on PFE1 of FPC 1 (ge-1/1/1) then it will be going via fabric hence on MX240 and higher there can be fabric limiting scenarios where full capacity cannot be acheived.
(2) if ingress and egress ports are on the same line card say PFE0 of the FPC 1(ge-1/0/1) receives the traffic and egress is also PFE0 of FPC 1(ge-1/0/2) then yes it will be 50 Gig each because Fabric will not come into flow then.
Thanks,
Shina