I had to dig a bit for these numbers into some of my tests but here goes:
Remember that the Mossie is only carrying 1K externally, the other 1K internally which only adds about 1mph of drag. They do have drag, 10mph worth, 5mph/bomb, but the bombs are also smaller. It's hard to compare that to something with two 1,000lb bombs hanging in the breeze, but anyway here are some other aircraft to consider that have the same 2K (all external @ sea-level) load carrying:
P-51D, 33mph penalty, 16.5mph/bomb
F4U-C, 25mph penalty, 12.5mph/bomb
Fw190D9, 12mph/bomb (can only carry 1 bomb, centerline, 500kg)
F6F-5, 20mph penalty, 10mph/bomb
P-47D30, 22mph penalty, 11mph/bomb
Typhoon, 17mph penalty, 8.5mph/bomb
P-38, 15mph penalty, 7.5mph/bomb
So, the P-51 is a little higher than most, it would appear the average is more about 10-12mph/bomb for 1,000lb type ordinance (or 500kg). I threw in the Fw190D9 although it only has a single 500kg, but it added half the drag that two bombs would so it came out to the same mph penalty/bomb. If anything, I think the Bf110G2 is a bit of an exception, I seem to remember the drag on the 1000kg option being rather low (more like 3-4mph/bomb) but I don't have those stats with me so I can't be too specific ( I think the mounting on those was different too, close together on centerline).
Move that to an abitrary 10K (as altitudes can favor one aircraft over another) and we get:
P-51D, 38mph penalty, 19mph/bomb (397->359)
Typhoon, 22mph penalty, 11mph/bomb (381 ->360)
P-47D30, 26mph penalty, 13 mph/bomb (362 -> 336)
Mossie, 11mph penalty, 5.5mph/bomb (367 -> 356)
F4U-1C, 28mph penalty, 14mph/bomb (354 -> 331)
Remember though, the Mossie is carrying two 500lbrs, not two 1,000lbs out in the breeze so you would expect there not be as much drag. ALL the stats show a drag increase of about 2-3mph combined for both bombs, barely worth mentioning honestly. The P-51D certainly suffers no more than a Typhoon at 10K, maybe slightly less. Figure that to compare the Mossie fairly you'd have to double the numbers for it, so 22mph and 11mph/bomb, 2mph off the P-47, 3 off the Hog-C, and tied with the Typhoon.
On the climb issue, the C-Hog can maintain 2,500ft/min with 2K, right up through 10K (it varies less than 100ft/min throughout). The P-51D starts slower (2,250ft/min) and surges a bit to (2,650ft/min) in the 5-9K range. The Typhoon starts stronger (2550ft/min) but drops off steadily till 10K (2,000ft/min). The Mossie is more like 3,100ft/min dropping to 2450ft/min by 10K. That said, that's with only 1,000lbs of ord, not 2,000 (I only have 1 test that had only external ord, no internal) so I would expect those numbers to drop a bit with some extra weight. The tests Karnak did include rockets too, those are real killers for performance, something like 1-2mph/rocket in most cases. I didn't include rockets because that unfairly weights the tests a bit (although for Karnaks purpose it was entirely appropriate to include them).
So, looking at the numbers, I don't see anything really amiss. The Typhoon pays a little less penalty for 1K bombs than the average (say 3-4mph total), but the P-38 pays even less. The Mossie, well, it's hard to compare that as it's packing ordinance much differently. It still follows the trend though of losing about the same amount/lb of external carriage, the fact that half the load is internal is an advantage (as you would imagine it should be). Simple differences in bomb-placement on the airframe could account for these small differences.
-Soda
