I have two SE/30 and recently equipped both of them with 64 MB from this source: https://www.amazon.com/-/de/gp/product/B00FAYV3NO
I found the price reasonable and with more than 32 MB you can add a nice ram disk, so I can recommend the 64 MB.
Boot time has increased by a few seconds but not dramatically. As I found out in another thread here the large ram increases boot time _before_ the happy mac. The Mac still boots up with 4x16 MB on bank A but it can only make use of more than 8 MB with mode32 installed. When it comes to large amounts of ram the Rom Initiator would only be needed for the latest APPLE UNIX A/UX 3.1.1, which needs a 32 bit clean rom. Otherwise it is not necessary.