Publicly available ASM sizing guide

Any recommendations then for sizing ASM?

Check out this report - should give you realistic data on what can be achieved with 10200 appliance and ASM as a guideline:

https://interact.f5.com/rs/f5/images/Web%20Application%20Firewall%20Product%20Analysis%20-%20F5%20Big-IP%20ASM%2010200.pdf

Also the F5 product datasheet contains detailed specs for each platform, again useful as a guide to understand the maximum number of Layer 7 connection / SSL terminations:

https://www.f5.com/pdf/products/big-ip-platforms-datasheet.pdf

Talk to an F5 rep for a more detailed ASM sizing. It will greatly depend on your requirements. For example, do you need FIPS/HSM processing? How many applications are you trying to protect, which features will you need? Will applications you are trying to protect contain credit card data and require DataGuard feature? Something like WebScraping can significantly impact the performance as well, any specific need for custom iRules etc... if the website is a simple brochureware with a contact form its protection (and sizing) requirements will be completely different from an e-commerce site like Amazon...