As a point of reference:


PICAXE Chip Type Label on Chip (DIP) Label on Chip (SM) Advanced Technical Details
PICAXE-08M2 PICAXE-08M2+ 12F1840 Microchip Datasheet
PICAXE-14M2 PICAXE-14M2 PIC16F1825 Microchip Datasheet
PICAXE-18M2 PICAXE-18M2+ PIC16F1847 Microchip Datasheet
PICAXE-20M2 PICAXE-20M2 PIC16F1829 Microchip Datasheet
PICAXE-20X2 PIC18F14K22 PIC18F14K22 Microchip Datasheet
PICAXE-28X2 PIC18F25K22 PIC18F25K22 Microchip Datasheet
PICAXE-40X2 PIC18F45K22 PIC18F45K22 Microchip Datasheet