That may be true but a lot of the other fighters (especially in 1939-43) weren't really all that good at a varity of roles. P-40s didn't do well at intercepting anything flying at 20,000ft or above for example, let alone trying to escort B-17s or B-24s unless they were flying low and close to home.
Well, I agree with that with some qualifiers. P-40s appear to have worked much better for the defense of Darwin than the Spit Mk Vs did, (and these were the early ones with the critical altitude around 12k ft) and the difference seems to be largely down to range / endurance. They could form up, climb laboriously up to altitude, and fly out to intercept the incoming aircraft and still have enough fuel to make multiple attacks and still make it back to base.
P-40s were notoriously bad at escorting heavy bombers, and they were tried for this task a few times, mainly with B-24s, both in the Pacific and the Med, with poor results.
Merlin powered P-40s were used in the Med with considerable success to escort medium bombers, in fact one of the FG there was assigned to the main B-26 bomber group, and they did really well. P-40N and M were used in the pacific and CBI to escort bombers and transports (notably over 'the hump') again in spite of having to fly at relatively high altitudes.
Generally speaking, I think you wouldn't want this plane to escort any heavy bombers.
A Spitfire V was shorter in range than a P-40 but it took rougly 2/3s of the time to get to 20,000ft and when flying above 20,000ft it had around double the rate of climb.
Depends on the types, but generally Spit V had an excellent climb rate. Early "Kittyhawk" P-40s as I previously mentioned, had a critical altitude down around 12,000 ft, Tomahawks were a little better, at about 15k. Merlin (F and L) types had a critical altitude at just under 20,000 ft so were good up to about 2,5000 or so. N and M (Allison) model had around 16-17k and were ok up to about 20k.
Now for all the "early long range Spitfire" fans see.
for times with and without a 90 gallon tank. Granted the tank has drag but we can pretty quickly figure out that the Spitfire V could loose around 200 fpm of climb even with a 45 gallon extra fuel load. and since at 26,000ft the climb rate was only about 1400fpm to begin with losing 10% or more due to to even 45 imp gallons extra fuel might not have been popular.
Now a MK IX Spit could climb (proving ground) at a bit under 2400fpm while carrying at 30 gallon tank at "Normal" (12lbs boost) rating.
Now in late 1942 which Spifire do you want to try escort for American B-17s in the mid 20,000ft area of the sky? Even if only over Holland
The Idea of an escort fighter is to actually provide an escort to the bombers, not provide alternative targets for the enemy to shoot down.
Simply flying along with or over the bombers isn't enough, the escort fighters need to be able to fight the enemy intercepters with at least some degree of success even if not shooting them down a 1:1 ratio.
I really wasnt' ever thinking of using Spitfires to escort B-17s or B-24s, at least not as the main escort, though if you had say, Spit VIII range plus a little extra from streamlining etc., it could be quite helpful in covering the return leg of a bombing raid. They did use Spits for this role, but if you had double the range that could really help.
However, I really think Spits would have been more effective both as interceptors, (especially with Radar / integrated defense system) and as tactical fighters, fighting over the various battlefields, if they had say 50-100% more range, and I think that was probably technically feasible. Whether it was feasible in industrial terms is unclear to me.