matched pair vs dual BJTs
several issues here:

the thermal timeconstant depends upon the distance between the emitters of the two transistors

The smallest distance for bipolars casually thrown onto silicon, perhaps in a 5-transistor array like CA3046, is 20 to 50 microns. Harris Semi produced(s) a high-speed variant, which of course will have a new layout.

Given the thermal timeconstant of 1 cubic meter of silicon is 11,400 seconds, and the thermal timeconstant of 10 microns is (1 meter/10micron)^2 faster or 10^10 faster, or 1.14 microseconds, you should not expect ultra-high-speed pulse processing to benefit from thermally-tracking bipolars.

Perhaps ComLinear opamps (long ago acquired by some other semi company) realized this, and laid out their input diffpair devices in very tight physical patterns, so the 2 emitters were very close. 

And now the second thought: you can cascode the devices, to reduce the Vce and thus reduce the self-heating. You might also adjust each Vce slightly as Ic varies, and thus keep the Ic * Vce constant in each of the two diffpair devices.

For this last --- keeping the Ic * Vce constant --- go review the translinear principle of Barry Gilbert.

[had an error: should have been cascode; I first wrote cascade]