igglebert:My experience is that you need to spend over a £1k to get decent floorstanders.I'd agree.
Depends on what you think is decent, but I recently heard a pair of Q Acoustics 1050i's and was very impressed by the sound produced by these relatively cheap speakers.The 1050's may sound good to some, and i can understand why, but if you compare them to something like the RS1's, they'll blow the 1050's out the water with their mid and treble detail, imaging, soundstage depth, bass control etc etc, and you get a nice wood veneer thrown in for good measure. As igglebert states, to get similar qualities from a floorstander that you get from a £500-800 standmount, you have to spend nearer the £1500 mark.
Because standmounts have smaller cabinet panels, they're less prone to cabinet boom, which in turn tends to give a less 'coloured' view of what's going on, producing a far more accurate presentation, giving a more 3 dimensional image. As they're smaller, material costs are smaller, so you tend to get better quality drivers/crossover and finishing. The only thing you have to take into account is a quality pair of stands, which won't be cheap at about £150/200.
A floorstander will utilise the space below a standmount that isn't being used, and look more attractive than using most stands. The extra cabinet volume will give extra depth, but this will need extra cabinet bracing which comes at a price. Whether they give extra punch is debatable, as some feel standmounts give a more dynamic punch as they sound faster due to the reasons listed above. But they will give higher SPL's with more, and deeper bass. As I said, because of the extra bass and volume floorstanders give, more money needs to be spent on counteracting the drawbacks this brings.