What is the difference between 'speculative', 'hypothetical' and 'conjectural'?

What is the difference between 'speculative', 'hypothetical' and 'conjectural'?

A hypothesis in a scientific sense is an idea based on existing evidence, that can be tested. Speculation isn't necessarily based on anything, and may not be provable.

Speculative is based on arbitrary assumptions, while hypothetical is based on certain priori reasoning or could also be imaginative.

Update: 1

Speculative is often used in context of betting and waging:

His investments in crude oil are speculative - they are based on assumptions that middle east crisis may further intensify.

Generating something hypothetical is a good tool in scientific research, proposals and education:

Professor, while teaching to his students, said, "Imagine a hypothetical situation where you find five bills of $100 lying around..."

No one seems to have addressed "conjecture", which seems to be midway between "hypothetical" and "speculative". It is an opinion or idea based on limited/incomplete information (Merriam-Webster.com and thefreedictionary.com). So, one might begin with some wild speculation, which after some brainstorming leads to a conjecture, having one gather all available information to form a hypothesis.