The first RAF raid to target a city rather than individual military or industrial targets within a city was the raid on Mannheim on the night of the 16/17th December 1940.
ie, after approx 20,000 British civilians had been killed in German bombing of London, Coventry, Liverpool etc.
This is of course complete rubbish. The USAAF was tasked with the (so called) precision bombing of German war industry by day.
The largest death toll of any raid or short group of raids was Hamburg. Dresden is possibly second, but the USAAF managed to kill 25,000 in Berlin in a single raid in Feb 45, without any help from the RAF.
First Mosquitoes would illuminate the target area, followed by an initial flight of Lancasters that bombed key road junctions to hinder relief efforts and the fire brigades, then the second wave of Lancs would drop thousands of small bomblets that shattered windows and holed rooftops to create good ventilation for the fire, then the final group of Lancs would drop thousands of small phosphor fire bombs and/or napalm setting the city ablaze.
The RAF used pathfinders to mark the target, followed by the main force with a mix of large HE blast bombs and incendiaries. The RAF didn't use small bomblets to shatter windows and hole rooftops, the only small bomblets the RAF used were the incendiaries.
As to bombing key road junctions to hinder rescue efforts, could you give a source for this? The pathfinders put the markers as close to the designated target area, the rest of the bombers bomber the target markers, nothing else.
The whole purpose of the pathfinders was to mark the target accurately, are you really suggesting the RAF had the accuracy to bomb individual road junctions around a city by night?
The attack on Dresden was in my opinion the worst of the RAF firebombing not only due to the number of civilians killed, but mostly because it was totally wanton. The estimated death toll ranges from 25.000 to a quarter of a million civilians killed.
The best estimates of the death toll are 25 - 35,000.
The 250,000 figure comes from a forgery of a German report on the bombings. The forgery, dated 22nd March 45, claimed 202,040 bodies had been found, and the death toll was expected to reach 250,000.
In 1965 and 1966 the real police reports surfaced.
On the 15th March the Dresden police issued a report saying as of 10th March 18,375 bodies had been recovered.
On the 22nd March the Berlin police issued a report giving the same 18,375 confirmed dead, and expecting the final death toll to reach 25,000.
On 3rd April the Berlin police issued another report saying 22,096 confirmed dead.