Variable Shipping providers

I have had this issue for a while: I use the (paid for) Royal Mail Shipping extension which works well for most things but if my customer order anything over a 1kg weight, my supplier automatically sends it by courier, rather than the postal service. I need to be able to choose a different extension (one for a courier) if the weight of the order goes above 1kg. Using your table rate plugin, will I be able to do that? Is it possible to have similar to this:
IF weight > 1kg, THEN use THIS extension to calculate/display shipping cost options
OR IF weight <= 1kg THEN use THAT extension to calculate/.display shipping costs
?

In hope….