firstly, all 1/8th buggies are 'basically' the same, the chassis layouts, the drivetrain, etc, but these particular 2 are almost identical, even sharing the majority of parts.

There is not really anything else inside your budget that is worth having. There are cheaper cars that will be disappointing, and there are better cars that are more expensive. Even if you raised the budget another 50 pounds, these would still be the best choices, and I would say spend the extra money on servos/engine/whatever.

You should not have a problem with the diffs on any of these cars. Most 1/8th buggies need no upgrades as such. You can upgrade some of the plastic and metal parts to carbon fiber, but you would not do that unless you were racing, and you would not race with a 300 quid RTR. See what I'm saying? Get a Virus or a Hyper 7, both are great for the money, there is no need to look further for the kind of money you are talking about. When you have SIX hundred pounds to spend, we can talk again

As lez mentioned, the Kyosho cars are also very good for the money...All three of these cars will serve you well. I would lean away from the Hobao, only because it does not come with a 2.4Ghz radio, which you should consider essential.

http://www.apexmodels.com/gbu0-prodshow/31295T2.html

The Hong Nor X1CRT is also a good car, but once again, no 2.4Ghz radio.