If you run backups outside of business hours, any impact on pool hosts cpu/memory performance is likely irrelevant (and limited by how many resources the XO is provisioned with anyway). The bigger potential impact is likely on your production storage, which again could be irrelevant outside of business hours.
However, if you want to perform backups more frequently and/or during business hours, in my experience the storage performance is the more likely to suffer noticeable impact. Unless your hosts are very highly utilized the additional cpu/memory load on a single VM shouldn't tip the scales. And at 500MB/sec your network shouldn't struggle either (I am assuming 10+Gbps links to get that speed).
And regardless of backing up during or outside business hours, or how long your backup window is, always consider the restore times! Performance of backup storage is always low priority until something needs to be restored If your backup takes 8 hours your restore will take 8 hours. Or longer. Don't cut any corners on backup storage, it is very important!