Cain Marko wrote:2 tons more payload.
4 tons extra internal fuel
Titanium bucket cockpit
Terrain following radar.
Btw It was in reference to A10 fantasy exhibited here. not as a comparison to mki. Note that it will have much more commonality with mki too.
The cockpit adds more weight and arguably you might want to debate adding more defensive aids for that trade-off.
TFR is no big deal. A mode can be added to most ESA radars.
Su-30 MKI has 9640 kg internal fuel. The Su-34 has 12,100 kg. That's approx 2700 kg not 4000 kg.
However, also consider: Empty weight is 18,400 kg. The Su-34s is 22,500 kg, 4000 kg heavier.
Both carry similar rated engines.
The drag on the Su-34 is considerably higher if you look at its profile.
The point is it needs the extra fuel, via both internal tanks and additional DT to provide it long legs and its extra weight, aero trade-offs for that crew comfort, come at a significant price of aero performance (the Su-34's acceleration, top speed, maneuverability all drop).
I'd rather work on adding wet wings to the Su-30 MKI design, better powerplants, redesign/upgrade the structure to be even lighter, new avionics, ECM. Not add a completely new aircraft to the IAF for limited gains. Literally all the munitions that can be carried by the Su-34 can be carried by the Su-30 MKI.
You can think of getting Su-34s if the Russians work with you on making an EW variant. That's where that crew's extra room, freedom of action will count as versus operating expensive EW from a cramped cockpit.