1.0.0.621 Catapult (OLD) - 14 
+10% vs Cities (PROMOTION_CITY_SIEGE by Default)
+35% Max vs Cities (w/PROMOTION_SIEGE)
1.0.1.135 Catapult (NEW) - 11
+30% vs Cities (PROMOTION_CITY_ASSAULT by Default)
+55% Max vs Cities (w/PROMOTION_SIEGE)
PROMOTION_CITY_ASSAULT and PROMOTION_CITY_SIEGE are not lost with upgrade
OLD Catapult vs Cities = 15.4
NEW Catapult vs Cities = 14.3
MAX OLD Catapult vs Cities = 18.90
MAX NEW Catapult vs Cities = 17.05
For Cannons and later (upgraded) they will have both PROMOTION_CITY_ASSAULT and PROMOTION_CITY_SIEGE
For 1.0.1.135, siege units upgraded from pre-cannon units will have a +30% vs cities.
MAX Upgraded NEW Cannon = 42.90
(26 * (1 + (0.10 + 0.30 + 0.25)))
MAX Upgraded OLD Cannon = 35.10
(26 * (1 + (0.10 + 0.25)))
Promotions available for Siege units:
PROMOTION_EMBARKATION
PROMOTION_DEFENSIVE_EMBARKATION
PROMOTION_INSTA_HEAL
PROMOTION_ACCURACY_1 (Open Ranged Attack +20%)
PROMOTION_ACCURACY_2
PROMOTION_ACCURACY_3
PROMOTION_BARRAGE_1 (Rough Ranged Attack +20%)
PROMOTION_BARRAGE_2
PROMOTION_BARRAGE_3
PROMOTION_SIEGE (+25% City Attack)
PROMOTION_VOLLEY (+25% Attacking Fortified Units)
PROMOTION_COVER_1 (+25% Defense against Ranged Attacks)
PROMOTION_COVER_2
PROMOTION_MARCH
PROMOTION_LOGISTICS (Extra Attack and Can Move After Attack)
PROMOTION_RANGE
PROMOTION_INDIRECT_FIRE
PROMOTION_MORALE
PROMOTION_FASTER_HEAL
CONCLUSIONS
Pre-Cannon Siege Units
Weaker vs Units and Cities post patch
Cannon Siege Units and above
Same vs Units post patch
Default Siege vs Cities same post patch
Upgraded Siege vs Cities +30% post patch
Keep those old siege units alive!
COMMENTARY
I can't help but think that Firaxis' intent was to keep the pre-Cannon values the same when attacking cities, but they forgot about the +10% vs cities all siege units get from PROMOTION_CITY_SIEGE.
For example, pre-Cannon siege units have access to a new promotion, PROMOTION_CITY_ASSAULT. This grants +30% vs Cities and replaces PROMOTION_CITY_SIEGE (which gave +10%)
Catapult was 14 and is now 11 [11 * 1.3 = 14.3 vs Cities/11 vs Units]
Trebuchet was 20 and is now 16 [16 * 1.3 = 20.8 vs Cities/16 vs Units]
Ballista was 18 and is now 14 [14 * 1.3 = 18.2 vs Cities/14 vs Units]
This works well to keep the strength vs Cities the same as pre-patch, but weaker vs units, assuming pre-patch, siege units didn't have +10% vs cities.
To accomplish what I think they intended, they need to buff PROMOTION_CITY_ASSAULT +10% (making it +40%). As it is now, pre-cannon siege units are inferior to post-patch in every aspect, and only have an advantage vs cities post-cannon, if you can keep them alive long enough to upgrade them.
One unintended consequence of the buff would be that Songhai Cavalry would have +40% vs Cities, since they use PROMOTION_CITY_ASSAULT. Originally, pre-1.0.1.135, they were the only unit to use this promotion...

+10% vs Cities (PROMOTION_CITY_SIEGE by Default)
+35% Max vs Cities (w/PROMOTION_SIEGE)
1.0.1.135 Catapult (NEW) - 11

+30% vs Cities (PROMOTION_CITY_ASSAULT by Default)
+55% Max vs Cities (w/PROMOTION_SIEGE)
PROMOTION_CITY_ASSAULT and PROMOTION_CITY_SIEGE are not lost with upgrade
OLD Catapult vs Cities = 15.4

NEW Catapult vs Cities = 14.3

MAX OLD Catapult vs Cities = 18.90

MAX NEW Catapult vs Cities = 17.05

For Cannons and later (upgraded) they will have both PROMOTION_CITY_ASSAULT and PROMOTION_CITY_SIEGE
For 1.0.1.135, siege units upgraded from pre-cannon units will have a +30% vs cities.
MAX Upgraded NEW Cannon = 42.90

MAX Upgraded OLD Cannon = 35.10

Promotions available for Siege units:
PROMOTION_EMBARKATION
PROMOTION_DEFENSIVE_EMBARKATION
PROMOTION_INSTA_HEAL
PROMOTION_ACCURACY_1 (Open Ranged Attack +20%)
PROMOTION_ACCURACY_2
PROMOTION_ACCURACY_3
PROMOTION_BARRAGE_1 (Rough Ranged Attack +20%)
PROMOTION_BARRAGE_2
PROMOTION_BARRAGE_3
PROMOTION_SIEGE (+25% City Attack)
PROMOTION_VOLLEY (+25% Attacking Fortified Units)
PROMOTION_COVER_1 (+25% Defense against Ranged Attacks)
PROMOTION_COVER_2
PROMOTION_MARCH
PROMOTION_LOGISTICS (Extra Attack and Can Move After Attack)
PROMOTION_RANGE
PROMOTION_INDIRECT_FIRE
PROMOTION_MORALE
PROMOTION_FASTER_HEAL
CONCLUSIONS
Pre-Cannon Siege Units
Weaker vs Units and Cities post patch
Cannon Siege Units and above
Same vs Units post patch
Default Siege vs Cities same post patch
Upgraded Siege vs Cities +30% post patch
Keep those old siege units alive!
COMMENTARY
I can't help but think that Firaxis' intent was to keep the pre-Cannon values the same when attacking cities, but they forgot about the +10% vs cities all siege units get from PROMOTION_CITY_SIEGE.
For example, pre-Cannon siege units have access to a new promotion, PROMOTION_CITY_ASSAULT. This grants +30% vs Cities and replaces PROMOTION_CITY_SIEGE (which gave +10%)
Catapult was 14 and is now 11 [11 * 1.3 = 14.3 vs Cities/11 vs Units]
Trebuchet was 20 and is now 16 [16 * 1.3 = 20.8 vs Cities/16 vs Units]
Ballista was 18 and is now 14 [14 * 1.3 = 18.2 vs Cities/14 vs Units]
This works well to keep the strength vs Cities the same as pre-patch, but weaker vs units, assuming pre-patch, siege units didn't have +10% vs cities.
To accomplish what I think they intended, they need to buff PROMOTION_CITY_ASSAULT +10% (making it +40%). As it is now, pre-cannon siege units are inferior to post-patch in every aspect, and only have an advantage vs cities post-cannon, if you can keep them alive long enough to upgrade them.
One unintended consequence of the buff would be that Songhai Cavalry would have +40% vs Cities, since they use PROMOTION_CITY_ASSAULT. Originally, pre-1.0.1.135, they were the only unit to use this promotion...