Ankit, RTO and RPO are usually used in backup scenarios. I can imagine that during restores (RTO) the storage is hammered hard because of all the data coming back from a restore and you might take that into consideration while designing your storage config, but I've never come accross such a scenario. Backing up however does cost performance on a regular bases, but then again: the research you did before creating the design should have revealed that and you should have designed your storage to be able to handle the extra I/O during backups. If you want backups to go faster, you should make sure that you're looking at the right bottleneck. Using an old LTO-1 tape drive will not help you getting anywhere near to backuping up at 750GB per hour. Look at all components if you want to create a new design (and you have the time for it). If time is the issue, make sure you make the right assumptions.
You could take into account that you want to be able to handle peak I/O without delays, but you can also consider to use a lighter config and you agree to have peak I/O times to flatline on 100% utilization for a bit longer if that saves you money. But be aware that doing so, production can feel the impact and it might even be undesirable to take a chance there.
Your advice about RAID10 for performance and RAID5 for Capacity + Performance is a rule of thumb. You should always investigate what you need. RAID5 isn't nessesarily bad for performance. If you have anough drives in a RAID5 configuration, this can even outperform a RAID10 config; simply do the math and see for yourself! Jon will publish a new post shortly and he will explain about how to do the calculation. If you have questions, ask! We can give examples if you want.
Thirdly: I can't say you need RAID10 for Exchange and RAID5 for a file server. Look at the previous explanation. Investigate before making decisions!