The short summary; ArP cap does affect ArP standings. Grim Toll + Mjolnir's is no longer as effective as before - for what trinkets you should use, consult a spreadsheet.
ArP is still the gem/gearing of choice for a combat rogue - unless I'm mistaken, even moreso for a mace-spec'd rogue, but the margin by which it is superior is
much smaller than it was prior to the cap.
The ArP AP weightings are dynamic - they change significantly based on how much ArP you have already - to evaluate the possibility of focusing on ArP, use a spreadsheet.
Here's a
good post illustrating the relative strength of gemming for ArP in BiS gear;