30W - All Tube
50W - Solid State
Is what I go by, for 'gigging'. But that's for combos roughly.
You can hook up your combo amp, into a cabinet. Or buy a head and connect it to the cabinet. The sound going through the cabinet is still changed (It isn't just louder) because of the speakers used, you can have Celestions, etc. and the cabinet itself.
Here's a nice quote:
Cabinet speakers use the combination of the speaker itself and the cabinet enclosure to produce an efficient means of sound reproduction. Depending on the requirement the cabinet can be "tuned" to enhance or diminish specific frequencies based on
With a 5W I would suggest upgrading to a Head and Cabinet, it might be a load to transport around but it's better than hooking it up to a cabinet. It's better left at home.