Gold Rush is designed as a series of choke points that the attackers must overcome. This good news for the defenders, because all they have to do is plug them up. The best method for plugging up choke points is sticky bombs, so use them to maximum effect. Placing them on the vertical post of a doorway out of sight from the other side is a great way to rack up kills and keep the enemy undermanned. Of course if you’re attacking, these are probably the doors you have to control to have any chance of winning. If they are being held well, then an über used to wrest them from the defence is usually and über well spent.
Quick note on the basics of the payload game mode. Keep in mind that the cart offers decent cover and acts as a dispenser if you’re close enough, so think of ways to make full use of this advantage. Attacking heavies can be continually rearmed as they plod alongside, and pyros can be free with their compression blasts, since ammo is never far away. Engineers also receive unlimited metal so long as they stand nearby. The defenders know the cart is the go-to point for most of the offensive team, so always keep the odd demoman or pyro keeping watch over it. Spies can also have a field day when the entire team is clustered around the cart facing forwards.
The CPs are generally very defensible, so it’s up to the attackers to find a way through. There is nothing more effective at disrupting defences than the übercharge. Popping a couple of these at the same time and coordinating an attack with the rest of your team is very effective and often the only way to win a stage. So medics, whatever you do stay alive, don’t do anything stupid. Your team needs those übers and dying with 90% of one charged is much worse than just 1 death. Try and coordinate with other medics whenever possible, and before you commence the big rush, make sure your team is ready and not half dead. Take out a target (e.g. a sentry gun), then set about cutting of defensive reinforcements – your teammates can deal with the folks behind you.
It will almost always be best to use your übercharges on demomen. No, soldiers, pyros and usually heavies are not effective against sentry guns. If there are enough of them, and there will be, you’ll get pushed back too much to get enough damage in, and this effect is exacerbated by the pyros who will swoop in and compression blast you away. A demoman can still be effective with all of this going on. Please, stop wasting your übers.
Although you might not wipe out the whole enemy team with an über rush, simply taking control of a foothold can be just as important. That’s right, Map Control. The key footholds are outlined in the previous strategy sections, and if you can get a level 3 sentry and teleport set up inside, it can put the defence very much on the back foot.
Although the cart must follow a single path, it’s very difficult to move unless the defenders are dealt with first. Other than the cart tracks, the will always be a couple of alternative paths. Attackers will do well to make full use of these, as a general rule of thumb splitting your team evenly between all available options for maximum flanking effect. This is much harder to defend against, and once the defenders are scattered, make an effort to prevent reinforcements rather than wasting time hunting down that sniper that got away.
Given the long, straight paths and multiple other routes, snipers and spies get to play more of a role than usual. Snipers are incredibly effective at locking down choke points for the defence, and so just as important for the attackers to prevent the defenders from doing so. Spies on the other hand can usually get a free run to some shadowy corner from which they can head back towards their own base, taking some enemies with them on the way. Keep your eyes out for teleporters.
Finally, class mix. Perhaps this should come earlier, since it’s generally the most important thing for teams to get right. I find people generally go the right classes on Gold Rush, but something along the lines of 3 medics, 2 engineers, 2 snipers/spies, and 5 out of soldiers, heavies, demomen and pyros will generally do alright. Just make sure the engineers keep those teleporters alight and the snipers/spies aren’t sucking. Because it’s very possible that they are.