Obviously you will not be able to project any meaningful sales figures easily, even if your product is not completely new: even then it would be risky to use other, similar products as examples since you would imply that your team, your sales strategy, your target market, etc. are all comparable for your assumptions to hold up, and I therefore would not recommend doing it.
The good news is that investors will not expect you to have precise forecasts - if they do, they do not understand the startup business. What they will (and should) expect, however, is that you have done your homework.
And by that I mean that you can test your market before even releasing your product. You will have one or more hypothesis about your business (growth and value hypothesis, for example that customers will like your product and also be ready to pay for it). Have you tested those hypothesis by engaging your customers? One of my clients is currently testing the market by launching a mock up page of his product and by measuring:
- how many people search for it?
- how many people actually go to the site and sign up?
- how many of those who sign up actually try to buy something?
The purchase part is still a stub and leads them to a page saying "coming soon" or something like that, but it gives him a good enough feeling for his potential sales in a defined market!
Since your product is B2B you may have different sales channels, but you can still use the same approach. There are similar testing methods for B2B businesses which will give you customer conversion metrics. Those you can then use to back up your sales projections, and I think those are also good enough for investors to understand that you know what you are doing.
If I can be of more help, let me know: contact me here