Road Bike speed versus Touring Bike

Does anyone know how much faster over 75 miles a £2k'ish carbon fibre road bike might be compared to a steel touring bike? I can't work out if it's worth having two bikes. I know the geometry is different but it seems fitness counts the most followed by a pair of light wheels. Any views gratefully accepted.
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The round trip was 17 minutes quicker on the Raleigh. I've not given enough information for anyone to determine what the quickest bike was all else being equal but I was much more comfortable over 72 miles for each trip with the kit in the pannier. That's why a tourer is a nice thing to have. I wouldn't be without either.
Whilst not a tourer, my audax bike is pretty hefty and steel. I have a few sets of wheels, and certainly the lightest set make a huge difference and I can keep up with people on carbon. I'm about to ride my first TT on it as well - might even take the mudguards off for that though! Whilst I too lust after a bit of carbon bling for my stable, I really don't need one. I don't race and my audax bike is plenty fast enough.
As ever, it's the engine that makes the most difference - If you're keeping up with your mates on carbon bikes, then I dare say, your engine is performing a little better than theirs!
http://www.bmj.com/content/341/bmj.c6801
It's written as a rather jokey academic paper for the Christmas issue of a journal, but makes some serious points.
Do you keep up? If so you have your answer.
If not, it is not the bike
From my experience, a lighter bike does lead to an increase in average speed but the effect is only really noticeable over longer distances.
Is it worth spending 2k on a new bike? No, if you just want to go a bit faster. Yes, if you have the money to spare and it will bring a smile to your face every time you ride it.