My advice is very simple: before purchasing a new carbon boom, be sure to have a good look at a Maui Sails carbon boom.
The 190-240 is quite heavy, but it's super stiff.The relatively high weight leads to a slightly different timing when jibing: the sail clew will start moving a bit slower, and will tend to arrive faster and 'drive' a bit further on the other tack, actually 'helping' slightly at sheeting in. Such effects are actually very very slight, and I am really stressing this; once used to the different feel, there really is no problem. Personally I use the 190-240 with slalom sails down to 5.9. Anyhow if one does not like the idea, and is more focalized on smaller size sails, the 170-230 is a great option: it's not got the oversized rear end, so it's more 'usual' stiff, but much lighter. If you look at pictures of Phil McGain testing sail protos, you'll see he uses it up to 7.0.