Frame delay is now set directly from the UI in the sliders menu, and it's stored per-game individually in MAME's config files (cfg folder)
In short you don't need to make specific inis for frame_delay anymore.
Sure you'll have to go through each game and set the slider, but it's good since several drivers updated by mamedev will have slightly different cpu load today anyway (many of your old f_d settings are probably wrong now)
note: apparently starting with 0.208 frame_delay is getting progressively more accurate but heavier too, which is something to keep in mind.