Put a number on it before you spend
Four tools for the decisions that usually get made on instinct: one measures what your real visitors experience, three do arithmetic on numbers you already have. Every one of them states what its output is not, and none of them ask for an email to show you the result.
Store speed check
What real Chrome visitors experienced on your store, kept separate from the lab simulation.
Storefront cost estimator
Eight questions about your store, one planning range built from real package prices — and what is inflating it.
Conversion revenue calculator
What a change in conversion rate is worth per month and per year — the ceiling on what it makes sense to pay for it.
Cart abandonment calculator
Your real abandonment rate, the value at stake, and what recovering a defensible share would be worth.
None of these model "faster site equals higher conversion". No honest coefficient for that exists for a specific store, so the scenario is yours to set — the tools measure, calculate and mark where a number stops being reliable, and nothing more.