I'm trying to beat 3 minutes - no easy task.
At the moment, there are too many dead bodies (mainly mine) in the way to have a good crack at it.
My best time is approx 3 mins and 7 secs or thereabouts.
Here is the you tube link for those who are interested.

https://www.youtube.com/watch?v=FX2IkPDrv64

That's a pretty interesting task.

You should try using nades more frequently in order to kill the low-hp groups of enemies. Some quad timing might help aswell .

I lose 0.5 sec when I switch from Grenade to shotgun. The switch is not instant. When I go to shoot the shotgun, it wont fire because its not ready, hence the delay.
The second to last Gunner drops grenades when he dies. When I run over the grenades, my weapon will switch from shotgun to grenade (not all the time).
When I fire again, its a grenade and the last gunner dies and so do I. Got caught heaps at this point til I figured it out. That's why I slightly pause at this point to check and switch back to shotgun.
My quad timing can be improved heaps - it's caused by pressure and the clock. I need to get 2 grenades on the Tank commander before quad expires.
Need to relax and not watch the clock.

That is impressive mate, the missions already hard enough to beat in solo and you go and speedrun it.
Gotta go fast!

Thank you Mik1. Much appreciated.
So now I have cracked 3 mins.
My time is approx 2 mins and 50 secs.
Tips if you want to win.
Quad damage is your most important ally. And with it is the shotgun shells.
Keep all you can for the quad run.
In the first part use ray gun and grenades and min shells.
Dont worry if you cant crack 3 mins. You still have 1 min to finish off Tank Commander with Ray gun. It's easy. Happy hunting.
Here is the link.
https://www.youtube.com/watch?v=rG_x2MDPN04

I have the avi file for those who want it. Let me know here.
Cheers

You tube said your video is jerky and wanted to fix it. Not knowing better, I said yeah and now you have missing frames and the info along the bottom is not always there.
Any how, I said no to this link.
https://youtu.be/WFn6LaYUTVM

Here is the link.
https://www.youtube.com/watch?v=rG_x2MDPN04

I deleted this. The next link is better.

I just came back from the club
and had a go. more than once..
its not easy espec when your pissed.
if u want, I'll help u thru the first part, the quad is all yours.
u have 30 secs and u must hit the tank commander with 3 grenades, all within the quad run.
its not easy to achieve this but thats where u need to practise. quad run is quad run. Very tough.
Want my help, let me me know.
Coopordie is the best,
cheers.

Nice, good job.

The next step is to speedrun the entire Quake II campaign.

OK Andrei, now its your turn to win 2 times. Coupla weeks should do it, eh.
Happy hunting.