From my experience topics from 1/2 are either completely, partially or very relevant to 3/4. That being said, there is also overlap between Spesh 1/2, 3/4 and Methods 3/4
Starting off with topics in 1/2 completely irrelevant to 3/4
Proofs: The methods of proof taught in 1/2 include induction, contradiction and direct proof. In 3/4, the only proofs you will need to know are direct and vector proofs
Sequences and series
Circle theorems
Topics partially relevant
Variation (ex. x is directly or inversely proportional to y): this is needed when modelling differential equations but I don't think I strong understanding of variation is needed to do well
Topics very relevant:
Vectors (almost exact same)
Complex numbers (exact same)
Mechanics
Kinematics
Trigonometry
Partial fractions
Statistics (quite a bit harder in 3/4)
Topics extended upon in 3/4
Calculus (wasn't even taught in 1/2 since it's taught so late in methods 1/2) especially integration
Vector functions
Reciprocal/inverse functions
And lastly, topics in 1/2 which overlap with methods 3/4
Statistics
Ironically, 1/2 has quite a bit of overap with uni maths (proofs, sequences and series)