The median pre-money Series A valuation for all WSGR startups is ~$8.0m [1], which is likely on the higher end.
Also, uncapped notes do not get diluted when raising your Series A, which is additional dilution for the entrepreneur.
For example, let's say you raise $5m uncapped notes with no discount. If you then raise a $3m Series A at a $8m pre-money valuation, you'll end up giving away more than 50% of your company, not counting interest or option pool. At a $15m pre-money valuation, you'll be giving away over 40% of your company.
Entrepreneurs should be equally careful with SAFEs.
[1] http://www.wsgr.com/publications/PDFSearch/EntrepreneursRepo...