In reply to Robert Durran:
> Apart from the fact that E4 onsight is way harder than 7a onsight (let alone redpoint!),
I'm not sure why you make such an assumption. There are plenty of trad routes that are easy to read from the ground: most crack climbs are an obvious example. There's also a fair bit of limestone sport that is really difficult to read, sometimes even when you're on the route. I'm not saying either is harder though. I think it depends on the route route and the type of rock, not so much on the protection needed.
> I suspect the vast majority of E4 climbers also sport climb (with most having no problem with 7a) but there will be large numbers of 7a and above sport climbers who don't (or barely) trad climb at all.Even if everyone agreed that a given sport grade was equivalent in difficulty to a given trad grade, I'm sure far more people would be climbing the sport grade.
I agree that's probably true. However that doesn't imply E4 is harder than 7a, simply because fewer climbers do them. Once you reach 7a and above there is far more sport climbing available to do in this country. But below 7a good sport routes tend to get thin on the ground. So there's more incentive to do trad routes at lower grades.
I pretty much only sport climb these days. I have had the odd period going back to trad. For me I find a brief period of adjustment is needed, not because it's harder but because it's different. A few days climbing is necessary to get used to placing gear, sizing up the right piece for a placements, getting used to falling on gear again, double ropes etc.