This link gives the Upper Limit for daily supplements...it seems rather low to me:

http://ods.od.nih.gov/factsheets/Mag...hProfessional/

This one also gives the same chart. It appears to me to be similar to the RDA chart...

Magnesium in people with healthy kidneys is excreted when in excess.

It is very difficult to say on an individual basis. I am having good responses from the lotion that I've been using. It works well for me. I seem to get "loose" on most of the oral forms.
You can also get magnesium from foods. Nuts and beans are good sources.

Keep in mind the ELEMENTAL values, and not total weight.
The citrate 300mg may be a total weight and not elemental.
And I think any product with a mixture of oxide with a chelate will be mostly oxide, and therefore not useful. It is inexpensive and keeps the pill size down. Most chelates are HUGE and difficult to swallow. So therefore you may not be getting the elemental value of magnesium from either product that is high enough for you.