The 4200 has the potential to be vastly better in power and yes it will be significantly lighter.
The Jimmy beats it on cool points though.
That said, there are sleeves, pistons, and rods available (special order) that should make the bottom end able to endure more boost than your particular blower can produce.
If you can get it for free or nearly free go 4 it, if nothing else you could sell it later (whole or 1 piece at a time).
