I do recommend the bonnet extensions, they will help in the summer.
The only downside is that you will get lots of "helpful" bystanders and other drivers kindly informing you that your bonnet is open!
I have the Librands crossover manifolds installed so there is probably a lot more heat generated from them than standard, and I find the standard fan (with an override switch), a deeper alloy radiator, and the bonnet extensions cope pretty well. Again the only downside is that the fan seems noisier than the engine at times.
