Hashcat speed problem?

[zl9801]

Test results for Web publishing:
---------------------------------------------
Hashcat 4.0.1,GTX 1070 Ti 
Hashmode: 0 - MD5
Speed.Dev.#1.....: 23360.6 MH/s (27.23ms)
Speed.Dev.#2.....: 23842.0 MH/s (26.73ms)
Speed.Dev.#3.....: 23729.3 MH/s (26.77ms)
Speed.Dev.#4.....: 23735.5 MH/s (26.83ms)
Speed.Dev.#5.....: 23672.9 MH/s (26.89ms)
Speed.Dev.#*.....:   118.3 GH/s

Hashcat 3.4.0,GTX 1080TI  8GB
Hashmode: 0 - MD5
32445.9 MH/s

My job:
-------------------------------------
Hashcat 4.0.1,GTX 1080TI 4GB

Command:hashcat64.exe -m 0 -a 3 ?a?a?a?a?a?a?a?a -O md5.txt

Session..........: hashcat
Status...........: Running
Hash.Type........: MD5
Hash.Target......: be7d821296f7e8dfb20ea057ac9b6980
Time.Started.....: Fri Oct 26 09:07:44 2018 (18 secs)
Time.Estimated...: Wed Oct 31 11:31:31 2018 (5 days, 2 hours)
Guess.Mask.......: ?a?a?a?a?a?a?a?a [8]
Guess.Queue......: 1/1 (100.00%)
Speed.Dev.#1.....: 15056.2 MH/s (6.84ms)
Recovered........: 0/1 (0.00%) Digests, 0/1 (0.00%) Salts
Progress.........: 275045679104/6634204312890625 (0.00%)
Rejected.........: 0/275045679104 (0.00%)
Restore.Point....: 0/7737809375 (0.00%)
Candidates.#1....: p_Yerane -> PfQ{\523
HWMon.Dev.#1.....: Temp: 41c Fan: 33% Util: 44% Core:1911MHz Mem:5005MHz Bus:4

Why does my speed differ so much from the network test results? Is there something wrong with my command-line statement?