1) Which kits? Do tell [img]smile.gif[/img] Test it yourself
2) In short, the greater HP is *probably* less than 9 (in the calculations below I have erred on the side of muchos generosity toward the multiclass and have rounded up most of the HP calculations in their favour). As this thread is based on powergaming, the character has just been imported from BG1 with 19 constitution.
As a Ranger/Cleric dual class, the character is able to achieve L22 Ranger/24 Cleric.
HP as follows:
9 x 10 + (9 x 5) = 135HP
13 x 3 = 39HP
Total 174HP
The Ranger/Cleric multiclass is able to reach L23/23 at 8 million experience points. The method for calculating multiclass HP is somewhat different.
Essentially for each level between L1-9 we get:
Fighter level 5HP per level (45HP)
Cleric level 4HP per level (36HP)
Plus 5HP Con bonus x 9 (45HP, may be less?)
Total: 126HP
Then we add:
Fighter 14 x 2 (28HP, may be less?)
Cleric 14 x 1 (14HP, couldn't be less

)
Which gives us a multi-class total of 168 vs 174HP. Difference of 6HP.
Upon investigating, I am DISSAPOINTED to reveal that there is no difference in the number of clerical spells between levels 23/25, meaning I can't use that as an additional bonus for the dual classed character (does tie in with the diminishing returns theme of this thread).
Ultimately though, greater HP and the ability to select a KIT swings makes the dual class the better choice for a POWER GAMER.