
To answer your question, we need to know a few things, and you need to watch out for some things with your purchase.
I guess we've already ascertained your budget, as cheap as possible

I'm guessing you want the tank more for fun, with driving about, over historic accuracy.
You've already learnt about that extra low weight being a benefit in the great outdoors.
With those in mind, the Heng Long with the newer 7.0 MFU certainly fits the low budget.
For driving about over rough terrain, the Heng Long M41 Walker Bulldog is one of the best runners, but the least historically accurate. Also the Heng Long gearbox ratios won't give you that smooth a slow speed drive.
When taking into account "metal" gearboxes, make sure they state steel gears, because there are some light alloy gears that aren't any better than nylon gears, and not much difference in weight.
I'm not fully verse with the 7.0 MFU, and therefore don't know how it would cope with a lot of extra added weight, because more weight would cause more Labour for the motors etc. There are more powerful replacement motors, but again, I'm not sure how the 7.0 MFU would cope with them.
It's all about how many amps that board can deliver, and I don't know the details of the upper limits.