Good point with the broom speed.
Real-world physics and game stats don't jive well with each other...never have. So instead of trying to guage the speed of an actor on a broom against a CGI background, let's use a benchmark instead. We can use something else on the screen that we already have stats for: the dragon. Here is my reasoning and my assumptions; let me know if you see anything wonky.
[SBLOCK=Assumptions and Stuff]The broom Harry is flying on in Goblet of Fire (Hermeione's Firebolt) is almost as fast as the Hungarian Horntail dragon he is evading, but not quite...we estimate that this broom is maybe, 10% slower. And since this dragon is (a) Huge in size, (b) breathes fire, and (c) isn't red, we will use an SRD young adult gold dragon as a benchmark.
Harry manages to evade the dragon not because he is faster, but because he has more maneuverability (broom: average, dragon: poor). He darts below the stands, does figure-eights through the castle towers, and eventually causes the dragon to crash into a bridge.
Dragon speed: Fly 200' (poor) 10% of 200 = 20; and 200 - 20 = 180. Therefore:
Firebolt speed: Fly 180' (average)
There are also two more brooms in the HP novels, the Nimbus 2000 and the Nimbus 3000. Since each new broom is described as being faster than its predecessor, we increase the speed by 10% each. Increasing the speed of the SRD's broom of flying is accomplished by adding the Haste spell at the same caster level as overland flight (cl 9), with command-word activation...but at half cost, since the rider doesn't gain the full benefit of a haste spell. Finally, for each subsequent "upgrade," we add 2,000 gp to the cost.
Does this sound fair?[/SBLOCK]
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So here are the revised broom stats.
[SBLOCK=Firebolt]This broom is able to fly through the air as if affected by an overland flight spell (average maneuverability) for up to 9 hours per day (split up as its owner desires). The broom can carry 200 pounds and fly at a speed of 180 feet, or up to 400 pounds at a speed of 90 feet. In addition, the broom can travel alone to any destination named by the owner as long as she has a good idea of the location and layout of that destination. It comes to its owner from as far away as 300 yards when she speaks the command word. The broom of flying has a speed of 90 feet when it has no rider.
Moderate transmutation; CL 9th; Craft Wondrous Item, overland flight, permanency, haste; Price 41,300 gp; Weight 3 lb.[/SBLOCK]
[SBLOCK=Nimbus 2000]As the Firebolt, above, except the broom has a maximum fly speed of 200 feet, or 100 feet when carrying 200-400 pounds.
Moderate transmutation; CL 12th; Craft Wondrous Item, overland flight, permanency, haste; Price 43,300 gp; Weight 3 lb.[/SBLOCK]
[SBLOCK=Nimbus 3000]As the Firebolt, above, except the broom has a maximum fly speed of 220 feet, or 110 feet when carrying 200-400 pounds.
Moderate transmutation; CL 15th; Craft Wondrous Item, overland flight, permanency, haste; Price 45,300 gp; Weight 3 lb.[/SBLOCK]
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And while I'm thinking about it, how about a broom-related feat?
Quidditch Flyer [General]
Your experience in the game of Quidditch has sharpened your flying skills.
Prerequisite: Ride 5 ranks
Benefit: your maneuverability when riding a flying broom improves one step (average becomes good, and good becomes perfect).