Some time ago last year, after being measured-up by Grant, I ordered a Strada Speciale frameset from Mercian Cycles, in lightweight Reynolds 853 Pro Team tubing, which I'm still waiting to have built, hopefully before this summer.
The intended use is as a (relatively) lightweight summer road bike, mostly for training, fast club rides and the odd sportive, but no proper racing and definitely no loaded touring or commuting on it (I have other bikes for that). At the time I ordered it with non-oversized tubing and threaded for a 1" headset. The frame size is 53cm centre-to-top (c-t), and I'm about 172cm / 72Kg.
Recently some fellow cyclists have hinted that I should have gone for oversized tubing, to reduce flex - but taking into account the frame size and my weight, is that really necessary? My power output is also currently relatively modest (recently tested FTP is about 200 watts), though I hope to improve on that a bit with more training.
Provided a frame comprised of non-oversized tubing would be stiff enough for me, I think I would prefer to stick with that, partially for aesthetic reasons (unlike some, I prefer the look of skinny tubing, at least on this sort of bike), but also think it would be less susceptible to denting, bearing in mind how thin 853 Pro Team tubing is in places....