Hash Rate and Internet Speed?

Hi

new to mining, so please bear with my question, as it maybe a simple over-site on my part.

I set up a small test gaming pc with 2 x gigabyte r9 270x windforce. This was mainly to get me up and running and able to alter settings before building a couple of larger more serious rigs.

I kept it simple and used the the two r9 270x as standard without any alterations. I was getting about 390 and 370 on each card most of the time, so about 750 was my average hash rate.

All seemed well, however when I looked at my stats on multipool after 30 minutes or so, it showed I was hashing at 14, and after mining for about 6 hours I had hash rates of between 10 and 40. I know from what other have said there is sometimes a difference but almost 90% does not seem right.

I was connected to the internet by a usb dongle with a sim card inside, not very quick but reasonable for surfing the internet. Do you think the different between my hash rates and what multipool were showing is down to a slow internet???

I did check my stats this morning and for a brief time it said I had 3000 or so dodge coins but they seem to have disappeared from my stats, any ideas about that also

any help welcome

cheers