hashcat 3.60 / hashcat 4.x many hashes
Hashes: 7268843 digests; 7268843 unique digests, 7268843 unique salts
Bitmaps: 23 bits, 8388608 entries, 0x007fffff mask, 33554432 bytes, 5/13 rotates
Rules: 1

hashcat (v3.6.0) W=3
Time.Estimated...: Mon Nov 13 08:33:39 2017 (21 hours, 12 mins)
Speed.Dev.#1.....:  1470.0 MH/s (4.85ms)

hashcat (v4.0.1-4-gfddb66eb) W=3 Optimized
Time.Estimated...: Tue Nov 14 00:06:25 2017 (1 day, 12 hours)
Speed.Dev.#1.....:   848.6 MH/s (0.93ms)

hashcat (v4.0.1-4-gfddb66eb) W=4 Optimized
Time.Estimated...: Mon Nov 13 20:05:49 2017 (1 day, 8 hours)
Speed.Dev.#1.....:   952.7 MH/s (7.55ms)

hashcat (v3.6.0) starting in benchmark mode...
Speed.Dev.#1.....:  7751.0 MH/s (60.57ms)

hashcat (v4.0.1-4-gfddb66eb) starting in benchmark mode...
Speed.Dev.#1.....:  7780.9 MH/s (60.63ms) W=3 Optimized
Speed.Dev.#1.....:  8096.2 MH/s (463.26ms) W=4 Optimized

hashcat 3 is faster than hashcat 4, if there are a lot of hashes.
what could be the problem?
I'm not clear from your post which tests are the ones that are for a large number of hashes.

And to clarify, by "Optimized" do you mean that you are using the -O flag?
judging by the tests the newer version the worse the performance. Sad
It is necessary to use old oclhashcat with which there are no problems.
yes used the -O flag
What is the GPU?
1080ti fe, if hashcat 3 slows down using hd6950 + oclhashcat 1.x, 2.x