CRX Si = mid/low 16 second car
CRX w/ B16A = mid/low 14 second car

So that would be a big difference. Getting a CRX HF would be good if you are a minimalist because its the lightest CRX (they got heavier each year so 88 is the lightest) and have less features. Si has everything you could want feature wise. HF and Si were also Multi Point Fuel Injection (used 4 fuel injectors) while the DX was Dual Point Fuel Injection (used 2 fuel injectors) so that means to you a swap into a DPFI car will be harder because of wiring, but its not that much harder, I've done it before, not that bad.