Like others suggested, don't waste your time or money with a 42" lawn sweeper. I am very satisfied with the powerflow system/MC519 cart on my 455; I also have an Agrifab Mow-N-Vac for some of the larger jobs.
The powerflow system and MC519 cart are extremely easy to mount and setup between uses. It definitely does a very good job at what it is designed to do. The MC519 uses 2 rear mounting points via the quick-tatch system and thus gives it exceptional maneuverability and stability. The cart does provide a lot of storage capacity (19 bushels), but it can still get full very fast. It's pricey, but extremely well made- I haven't had to replace a single part yet in 15 years of part time use.
Another item to consider would be a Cyclone Rake or a Mow-N-Vac. Our Mow-N-Vac has a 26 bushel capacity, but probably holds twice as much as the MC519 because the 5hp engine chips and shreds up all the leaves into tiny pieces, making it pack well. It's also nice having a detachable hose with tons of suction for those hard to reach areas and random piles of leaves. However, I have to be careful not to mow on hills or steeper areas when the cart is filling up because it is very top heavy. It's also more difficult to mount to the mower deck and requires occasional tweaking as you go. I probably only use it 3-4 times a year, but it's been worth every penny. Even with seldom use, the 5hp engine on the Mow-N-Vac still starts up first try every season and it is getting to be 6 or 7 years old now.
RubiconRider, since you still have about 7 months to prepare for leaf season, it might be best for you to search Craigslist and local ads for good deals on used units.
Here is a picture of inside my Mow-N-Vac to show you just how much it can hold.