Part of me wants to quote Spiderman and answer your question
Is memory latency still a key factor in computer speed? with
It never was.
But that would be dismissing a small sub class of operations that do happen if not all that often. Many tasks these days work with more than a single byte at a time, and often many of those bytes are next to each other.
If you have a task that works with a tiny piece of data from a random location then latency will be a significant factor.
If on the other hand you are dealing with blocks of data then latency will only really have an effect at the beginning of each memory block transfer and will depend on the memory transfer block size. Modern memories assume, like hard drives, that multiple continuous bytes will be required and will pre fetch and "burst" 8 words of data at a time. This burst means that the latency only applies at the start of the request, if the task actually needed those other bytes as well then it is already in the CPU cache ready to use at minimal latency.
Latency has an effect, but can be mitigated by CPUs by switching to tasks that are not waiting on memory accesses and by anticipating future memory requirements and queuing up memory requests.
Bandwidth has always been more significant than latency but latency can add an amount of inefficiencies while programs stall waiting for data.
There is a lot more to it than just 30% higher latency = 30% lower performance. For a majority of cases the effects of latency are mitigated by CPU caches, prefetching and other intelligent design.
This is also one reason why Intel advocate Hyperthreading and other technologies as improving high-demand multithreaded task performance. If you have two tasks running on a single core and one task stalls on a memory request then there is a good chance that the other task can make use of the CPU resources. Hopefully by the time that task stalls the memory requests for the first task will have completed and then that task can run again, thus making best use of all the CPU resource.