I assume you have access to classified information on both aircraft.
Photos are not classified. And you can tell a lot about its relative observability from its airframe.
Your 'stealthiness' assertion is baseless, although the pak-fa's intake inlets are not shielded yet, there is no guarantee that the J-20 has an overall lower RCS. The J-20 canards and wing geometry doesn't exactly guarantee anything. Further, a panel that is not plush with the rest of the aircraft can increase the overall RCS by a factor of 3, and one picture indicates that the J-20 does not have a plush panel.
The wing geometry does in fact play a big role. Read Bill Sweetman's articles.
Here is Bill Sweetman explaining some design aspects that allow the J-20 to be stealthy (here are direct quotes):
- "It has a low height triangle appearance from the front. This ensures a small radar signature from the front."
- "Wing body junction is clean."
- "Sharp chine line around forward fuselage."
- "Flat body sides are aligned with canted tails."
- "Saw toothed edges tend to break up the radar signature by absorption or redirection."
- "The flat lower fuselage is optimal for all aspect wide band stealth."
- "To keep radar waves from returning to the sending antenna, the leading and trailing edges of the wing and tail have identical sweep angles."
- "Many of the surface shapes of the J-20 are curves with constantly changing radii. These scatter radar beams in all directions instead of back to the radar source."
Here is what may impede the T-50's stealthiness when compared to the J-20:
- The T-50 does not have a smooth underside
- Lack of panel alignment
- Gaps around the inlet
- Spherical IRST
- (Continued below)
The J-20 also has (which the T-50 does not):
- DSI
- Frameless bubble canopy
- IR reducing tiles on the engines
- Possible plasma stealth technology
All of the above contribute to RCS reduction. T-50 does not use the measures.
As for weapons and fuel load this is utter rubbish, there is little information on both. And I wound be careful when proclaiming the J-20 to hold more fuel even if it may be a larger aircraft. Fuel capacity is directly linked to area, by this I mean available storage. The pak-fa has a very large wing area, furthermore, it does not have an curved intakes that take up room in the fuselage.
And engines efficiency coupled with factors such as drag and wing area dictate range. Fuel capacity alone means little when an aircraft has poor efficiency, high drag, ect.
The mere size of the J-20 can tell us a lot about its role and its configuration. The J-20 is most likely not an air superiority fighter, thus sacrificing speed for a larger fuel and weapons load. The fact that it will be using the most powerful engines in the Chinese arsenal further implies that it is a strike fighter.
The J-20 has a large wing area as well. Take a look at some photos if you want further proof.
Delta wing configuration provides less drag, one of the main reasons the Avro Arrow chose it to further its role as a high speed interceptor.
As for maneuverability, again, there is no information published on either aircraft and maneuverability is a vague word, are we taking about role rate, sustained turn rate, low speed maneuverability, high speed maneuverability? Looking at an aircraft it is almost impossible to determine its maneuverability, but we know several thing about the pak-fa that should give us an idea of just how maneuverable may be. The pak-fa's widely spaced engines coupled with TVC and widely spaced horizontal wings will insure that the pak-fa will have a very high role rate; likely higher than any other aircraft. Than we have LERX, a large wing areas, high T/W ratio and final fly-by-wire. The designer of the SU-35 were able to maintain at least the same performance of a canard set-up simply by improved fly-by-wire systems and better engines. Generally only Chinese and Pakistani members believe the J-20 is more maneuverable, most neutral parties with relevant aviation knowledge would disagree.
Looking at its airframe is possible to tell if it has at least a good chance at being a highly agile fighter.
The reason why Chinese chose the canard delta design in its J-10A (which defeated J-11A 6:0) is because of its enhanced maneuverability. The French, British, and Swedish also incorporated it into their fighters. The canards will definitely boost the J-20's maneuverability, while the deltas will decrease drag and increase performance in transonic and supersonic flight.
In fact, the main reason the F-22 didn't adopt canards for maneuverability is its contribution to RCS. With the J-20's plasma stealth technology, however, the problem is solved.
The 117 or the derivative based off of the 117 already has a 15% greater thrust with an additional goal of 10% greater trust. Supercruise is also mostly dependant upon an aircraft's drag and dry thrust.
Even if the 117S derivative was upgraded as you described, it would produce an afterburning thrust of about 155 kN. That is about the same as the WS-10G engines installed on the J-20 prototype, and far less than that of the WS-15 engine, which will become the production engine of the J-20.