A few things will likely change, depending on your equipment.
One change that may have escaped your attention (it certainly did mine the first few times) is that if you're decreasing the amount of top-off water, your hop utilization will increase. This means a more bitter beer if you just take the amount of hops you're currently using and multiply by 3/5.
Of course, good brewing software will account for this, which brings up an important question: How are you scaling your recipe? Excel? BeerSmith?