Yikes! If you can afford a 750, then you have enough money to "pin your hopes" on having all your files backed up on a seperate drive, no? That way you're not rolling dice on if your bits will still be there tomorrow or not.
I don't know the exact prices, but for the price of a 750 could you maybe buy a 250, a 400, and a USB2/eSATA enclosure? Use the 250 for storage, and put the 400 in the enclosure. Any backup program can automatically keep 1-2 weeks of differential backups on that 400, so if you ever lose the 250 (or more commonly: erase a file you wish you hadn't) you can get things back from any point in the last 7-14 days.
If you have 2 computers you could also have them back each other up over the network: that's what I do.
This probably isn't what you wanted to hear: but disk space is dirt cheap: disks are worth nothing. Knowing your data is safely protected on a seperate disk run by an automatic program that you don't have to think about is worth a lot.
This is assuming your data is important, and not disposable stuff you could easily get again with a P2P app: in that case buy the 750
(Oh, and this setup works nice over time as well: when you need more space you buy a large disk... make it your backup disk... and your old backup disk becomes you new storage space. Rinse and repeat as needed...)