cat5e and power cable

Preface

I FEEL like I should get a million results, but it seems my google-foo is not strong enough.
Please do not flog me with a stripped 6A cable if this has been asked before.

I don't do the wiring myself. I'm a one man IT dept. for an environment that I inherited.
New cabling is done by a third party.

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The heart of the matter

Everybody and their granny know that Moses actually had three stone tables, but he dropped one and nobody saw commandment 11 through 15.

Number 11, as we also all know, was "thy shalt not run thine ethernet cables and thine power cables in the same enclosure".

Sadly though, exactly that has been done in my company, everywhere.

Is this a quantifiable difference? Can I measure performance is lost somehow, or estimate this to some degree?

Example

This part may be entirely unnecessary.

I sit at a 4-way computer island. Below is a (probably too long) description of the situation.
Should I expect a big difference if I were to separate ethernet and power?

Code block is a top view, pound signs are our desks, dashes and pipe symbols are all the power and ethernet cables combined. Plus signs are where cables from different directions come together.
"P" is a printer shared by 2 users.

| | | | ####P#### +------------+---- ####P#### 

The total cable length from pc to switch is about 8 meters, and let's just say for the sake of ease that this is also the same length that ethernet and power cables run side by side.

Each workstation has 4 power cables (pc, dual monitors, dect phone charger) and 1 ethernet cable.
The printers also have 1 power cable and 1 ethernet cable.

All power cables go into 2 power strips, plugged into the cable trunk at the wall.
There are 10 electrical outlets at the wall, only these 2 are being used.

The ethernet cables obviously each go into their own jack, in the same cable trunk.
All ethernet cables are 5e, all power cables are... ehh.. black.
Switches are gigabit.

Am I being robbed of precious internets?

In other places of the room (you guys are going to love this) the ethernet cable runs alongside power cables of TL lights.

Final thoughts

So, should I use all my might and influence to get my company to renounce their evil ways?
If you separate them, by how far? Does it suffice to have them bound in 2 runs in the same conduit, with 10 or so mm in between, or do I really need individual trunks/conduits to have them centimeters apart?
Will my dl speed go from (random number, not tested lately) 10Mbps to 50 Mbps, or to 10.5Mbps?

Bonus question

Speaking of Mbps, how do you determine if people have an acceptable speed everywhere in the company, with varying use and many people doing many things?