Bike porn

Probably this, assuming you already have it fitted properly. Really cost effective upgrades, in terms of watts saved per pound spent, can often be made to tyres/tubes. If you have the wrong ones, £70 can buy you 10W at 30mph, a saving which might be impossible or hugely expensive on a wheel purchase, depending on your starting point. STIs won't make your bike faster, but they might be the difference between staying in the group and getting dropped, so definitely get those if you're road racing. After that, it's pretty certain that more aerodynamic wheels will make a bigger difference to your speed when you're alone/on the front than any modest weight saving, although you can shed quite a bit of weight of most older/stock bikes for not much money by well considered upgrades to bars/stem/ seat post.

It obviously depends on how fast and flat the ride is, but I thought aero wheels only really made sense on bikes needing to stay over the regulation 6.5kg. And if your bike is over that your nearly always best off shedding as much rotating mass as possible?