I don't really understand what you're trying to measure. I can make some comments about different things you might mean:
--- 1 ---
Say you are presented with a politician's speech on some topic, topic X. Your background vocabulary is such that, out of the unique lemmas present in the speech, you know about 7/8 of them.
Without a dictionary, you aren't that likely to be able to answer basic questions like "is this politician for, or against, topic X?". With a dictionary, this will improve.
--- 2 ---
If you need a dictionary for every word in a document, that means you don't know any of the grammar of that language, and regardless of how much dictionary access you have, you're not going to be able to understand the document.
--- 3 ---
If we're glossing over grammatical particles, and you're allowed to use a dictionary, then this is a question of speed. The differences aren't as significant as you seem to think. A major reason for this is that words get repeated; if you need to look up a previously unknown word the first time you encounter it, you probably don't need to look it up the third time. Your reading speed will start slow and increase very rapidly, as long as you keep reading about the same kinds of things (for example, because you're reading a single document).
Put another way, the process of starting to read a document will convert you from a stylized "every other word" to a stylized "every tenth word" within a short time.
--- 1 ---
Say you are presented with a politician's speech on some topic, topic X. Your background vocabulary is such that, out of the unique lemmas present in the speech, you know about 7/8 of them.
Without a dictionary, you aren't that likely to be able to answer basic questions like "is this politician for, or against, topic X?". With a dictionary, this will improve.
--- 2 ---
If you need a dictionary for every word in a document, that means you don't know any of the grammar of that language, and regardless of how much dictionary access you have, you're not going to be able to understand the document.
--- 3 ---
If we're glossing over grammatical particles, and you're allowed to use a dictionary, then this is a question of speed. The differences aren't as significant as you seem to think. A major reason for this is that words get repeated; if you need to look up a previously unknown word the first time you encounter it, you probably don't need to look it up the third time. Your reading speed will start slow and increase very rapidly, as long as you keep reading about the same kinds of things (for example, because you're reading a single document).
Put another way, the process of starting to read a document will convert you from a stylized "every other word" to a stylized "every tenth word" within a short time.