The latest thinking is that for slicks there is no real difference, a 35c is just as good as a 23c.
Which is a latest thinking which is not universally accepted, I would say it was a minority opinion.
It is also based on the often forgotten and totally unrealistic condition that the tyres are inflated to the same pressure.
So pump up your 35mm tyres to 110psi and enjoy.
People seem to be hanging on to "...at the same pressure..." bit that which while correct on its own, doesn't really give one a full picture of what makes tyres roll fast on real (UK?) roads.
Wider tyres have lower rolling resistance not just at the same
but at their optimal pressure e.g. using an excellent 15% tyre drop method.
The differences are very small on smooth surfaces but very obvious on bad roads where lowering the pressure can paradoxically reduce rolling resistance by allowing tyres to absorb road imperfections more effectively.
Comparing 23mm to 35mm tyres only makes sense only if using the same tyres at the optimal pressure. E.g. a 700x38C Marathon will be typically (but not always) slower than a 23mm Vittoria Corsa Evo NOT because it's wider but because it's designed as a touring not racing tyre. Hit the cobbles though and Marathons at half the pressure of skinny tyres are going to roll faster.
Going back to the OP question, I've been commuting and training on a 26" franken road bike with drop bars (the only road bike I've got) for over 2 years and I clock average speeds of 18.5-20.0mph on it. Shaven MTB tyres up to 2.10" wide don't seem to slow me down, quite the opposite http://bartthebikeman.wordpress.com/201 ... road-tyre/
In fact I've found that on New Forest roads a 2.10" wide 120TPI wide supple shaven XC MTB tyre at 20/30PSI rolls marginally faster than a 28mm Grand Prix road slick at 80/60PSI. That's based on many timed (stopwatch) runs not by feel. http://bartthebikeman.wordpress.com/201 ... -prix-mtb/
P.S. As for the popularity of certain opinions. Some people think, some just follow